Method and apparatus of scanning in wireless local area network system

ABSTRACT

A scanning method in a wireless local area network (WLAN) system is provided. The scanning method includes transmitting by a station a probe request frame via a channel, and receiving by the station a probe response frame from a target access point (AP) to respond to the probe request frame. The probe request frame includes at least one of information regarding a response reception time and preference information regarding the target AP.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of Korean PatentApplication No. 10-2011-0139937 filed on Dec. 22, 2011, Korean PatentApplication No. 10-2011-0146052 filed on Dec. 29, 2011, Korean PatentApplication No. 10-2012-0004095 filed on Jan. 12, 2012, Korean PatentApplication No. 10-2012-0005374 filed on Jan. 17, 2012, Korean PatentApplication No. 10-2012-0025299 filed on Mar. 13, 2012, Korean PatentApplication No. 10-2012-0026331 filed on Mar. 15, 2012, Korean PatentApplication No. 10-2012-0074226 filed on Jul. 6, 2012, and Korean PatentApplication No. 10-2012-0150982 filed on Dec. 21, 2012, all of which areincorporated by reference in its entirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a scanning method in a wireless local area network(WLAN).

2. Related Art

With the recent development of information communication technology, avariety of wireless communication techniques are being developed. Fromamong them, a WLAN is technology for wirelessly accessing the Internetat homes or companies or in specific service providing areas by usingportable terminals, such as a Personal Digital Assistant (PDA), a laptopcomputer, and a Portable Multimedia Player (PMP), based on radiofrequency technology.

Communication in a WLAN according to the IEEE 802.11 standard ispremised on that communication is made within an area known as a basicservice set (BSS). A BSS area may change according to propagationcharacteristics of a wireless medium, so a boundary thereof is somewhatindefinite. A BSS may be basically classified into an independent BSS(IBSS) and an infrastructure BSS. The IBSS refers to a BSS forming aself-contained network in which an access to a distribution system (DS)is not permitted, and the infrastructure BSS refers to a BSS includingone or more access points (APs), a distribution system, and the like, inwhich an AP is used in every communication process includingcommunication between stations (STAs).

When a STA wants to access a wireless network, the STA may use twoscanning methods including passive scanning and active scanning todiscover an accessible wireless network (e.g., a BSS, an IBSS, etc.),namely, an AP to which the STA is to be connected.

A passive scanning method uses a beacon frame transmitted from an AP (oran STA). Namely, when an STA wants to access a wireless network, the STAreceives a beacon frame periodically transmitted from an AP, or thelike, that manages the corresponding wireless network (e.g., a BSS, anIBSS, etc.) to discover an accessible wireless network (e.g., a BSS, anIBSS, etc.). In the case of passive scanning, the STA should wait untilwhen a beacon frame is transmitted from the AP, so much time may betaken for the STA to discover the AP. In general, a transmission periodof a beacon frame is 100 ms.

According to an active scanning method, an STA, which wants to access awireless network, first transmits a probe request frame and an AP (or anSTA), which has received the probe request frame, responds thereto by aprobe response frame. Here, every AP, which has received the proberequest frame, responds by a probe response frame, flooding of proberesponse frames occurs. Also, since the STA sequentially scans everychannel of a wireless medium, a scanning time may be lengthened.

Thus, a scanning method for reducing flooding of probe response framesand shortening time required for performing scanning is required.

SUMMARY OF THE INVENTION

The present invention provides an active scanning method and apparatuscapable of shortening an initial link setup time in a wireless localarea network (WLAN) system.

The present invention also provides an active scanning method andapparatus capable of reducing flooding of probe response frames.

In an embodiment of the present invention, a scanning method in awireless local area network (WLAN) system is provided. The methodincludes transmitting by a station a probe request frame via a channel,and receiving by the station a probe response frame from a target accesspoint (AP) to respond to the probe request frame. The probe requestframe includes at least one of information regarding a responsereception time and preference information regarding the target AP.

The information regarding a response reception time may includeinformation indicating a time that the station is available aftertransmission of the probe request frame to receive the probe responseframe as responses with respect to the probe request frame, as beingincluded in the probe request frame by the station.

When the information regarding the response reception time is includedin the probe request frame, the station may receive the probe responseframe from the target AP during the response reception time indicated inthe probe request frame, after transmitting the probe request frame.

The preference information regarding the target AP may include at leastone of first information indicating preference with respect to highthroughput (HT) capability of the target AP which responds to the proberequest frame and second information indicating preference with respectto very high throughput (VHT) capability of the target AP. In case thatat least one of the first information and second information is includedin the probe request frame, the station may receive the probe responseframe from the target AP satisfying the first information and the secondinformation.

The preference information regarding the target AP may further includeat least one of information indicating preference with respect to accessdelay of the target AP, information indicating preference with respectto link quality of the target AP, information indicating preference withrespect to an operating condition of the target AP, informationindicating preference with respect to a network of the target AP, andinformation indicating preference with respect to security of the targetAP. In case that the preference information regarding the target AP isincluded in the probe request frame, the station may receive the proberesponse frame from the target AP satisfying the preference informationregarding the target AP.

When the station generates intermediate scanning results with respect tothe target AP and discovers an AP to be associated based on thegenerated intermediate scanning results, the station may instructscanning abort in the middle of the scanning.

The method may further include selecting by the station a next channelto be scanned based on information regarding a neighbor AP included inthe probe response frame. The information regarding a neighbor APincludes at least one of an AP channel report and a neighbor report.

The information regarding a response reception time may further includeinformation indicating a time at which the station starts to receive theprobe response frame. In case that the information indicating a time atwhich the probe response frame starts to be received is included in theprobe request frame, the station may receive the probe response framefrom the target AP during the response reception time indicated in theprobe request frame starting from the time at which the probe responseframe starts to be received that is indicated in the probe requestframe, after transmitting the probe request frame.

The probe request frame may further include list information regardingan AP which is to respond to the probe request frame by using at leastone of an SSID (Service Set Identifier), a BSSID (Basic Service SetIdentifier), an MESHID (Mesh Identifier), an HESSID (Extended ServiceSet Identifier), and a Network ID of the AP which should respond to theprobe request frame.

The probe request frame may further include list information regardingan AP which should not respond to the probe request frame by using atleast one of an SSID (Service Set Identifier), a BSSID (Basic ServiceSet Identifier), an MESHID (Mesh Identifier), an HESSID (ExtendedService Set Identifier), and a Network ID of the AP which should notrespond to the probe request frame.

The probe request frame may include capability information regarding thestation, and the capability information regarding the station mayinclude at least one of extended capability information, high throughputcapability information, very high throughput capability information, andsecurity capability information.

The method may further include discovering by the station an AP to beassociated by receiving at least one of short beacon frames, measurementpilot frames, short probe response frames, probe response framestransmitted in a broadcast manner, and probe response frames transmittedaccording to a request from other stations.

In another embodiment of the present invention, a scanning method in awireless local area network (WLAN) system is provided. The methodincludes receiving by an access point (AP) a probe request frame from astation, and transmitting by the AP a probe response frame to thestation. The probe request frame includes at least one of informationregarding a response reception time and preference information regardinga target AP to respond to the probe request frame.

The information regarding a response reception time may includeinformation indicating a time that the station is available aftertransmission of the probe request frame to receive the probe responseframe as responses with respect to the probe request frame by thestation. In case that the information regarding the response receptiontime is included in the probe request frame, the AP transmits the proberesponse frame to the station during the response reception timeindicated in the probe request frame.

The preference information regarding the target AP may include at leastone of first information indicating preference with respect to highthroughput (HT) capability of the target AP which responds to the proberequest frame and second information indicating preference with respectto very high throughput (VHT) capability of the target AP. In case thatat least one of the first information and second information is includedin the probe request frame, when the AP satisfies the first informationand the second information, the AP may transmit the probe response frameto the station, and when the AP does not satisfy the first informationand the second information, the AP may not transmit the probe responseframe to the station or transmits a null probe response frame to thestation.

The preference information regarding the target AP may further includeat least one of information indicating preference with respect to accessdelay of the target AP, information indicating preference with respectto link quality of the target AP, information indicating preference withrespect to an operating condition of the target AP, informationindicating preference with respect to a network of the target AP, andinformation indicating preference with respect to security of the targetAP. In case that the preference information regarding the target AP isincluded in the probe request frame, when the AP satisfies thepreference information regarding a target AP, the AP may transmit theprobe response frame to the station, and when the AP does not satisfythe preference information regarding a target AP, the AP may nottransmit the probe response frame to the station or transmits a nullprobe response frame to the station.

The probe response frame may include information regarding a neighborAP. The information regarding a neighbor AP may include at least one ofan AP channel report and a neighbor report.

The information regarding a response reception time may further includeinformation indicating a time at which the station starts to receive theprobe response frame. In case that the information indicating a time atwhich the probe response frame starts to be received is included in theprobe request frame, the AP may not transmit the probe response frame tothe station until a time at which the probe response frame starts to bereceived is reached, and may transmit the probe response frame to thestation during the response reception time indicated in the proberequest frame starting from the time at which the probe response framestarts to be received that is indicated in the probe request frame.

The probe request frame may include capability information regarding thestation, and the AP determines whether to permit an association of thestation thereto when the AP receives an association request from thestation based on the capability information regarding the station. Incase that the AP decides to permit an association of the stationthereto, the AP transmits the probe response frame, and in case that theAP decides not to permit an association of the station thereto, the APmay not transmit the probe response frame to the station or may transmita null probe response frame to the station.

The probe request frame may include at least one of list informationregarding an AP which should respond to the probe request frame and listinformation regarding an AP which should not respond to the proberequest frame. In case that at least one of the list informationregarding an AP which should response to the probe request frame and thelist information regarding an AP which should not respond to the proberequest frame is included in the probe request frame, when the APcorresponds to the list regarding an AP which should respond to theprobe request frame, the AP may transmit the probe response frame to thestation, and when the AP corresponds to the list regarding an AP whichshould not respond to the probe request frame, the AP may not transmitthe probe response frame to the station.

Active scanning may be more effectively performed, so an STA can rapidlydiscover an AP to be associated, shortening an initial link setup timein a WLAN system. Flooding of probe response frames is prevented, thuseffectively performing active scanning. Also, the active scanningapparatus according to an embodiment of the present invention iscompatible with existing legacy equipment, so there is no need to modifyhardware of existing equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically illustrating an example of a wirelesslocal area network (WLAN) system to which an embodiment of the presentinvention is applicable.

FIGS. 2 and 3 are flow charts illustrating an active scanning method ina WLAN system.

FIGS. 4 and 5 are flow charts illustrating an active scanning method ina WLAN system according to an embodiment of the present invention.

FIG. 6 illustrates an example of information items included in aninclusion list according to an embodiment of the present invention.

FIG. 7 is a view illustrating an example of information items includedin an exclusion list according to an embodiment of the presentinvention.

FIG. 8 is a view illustrating formats of information elements includedin the inclusion list or the exclusion list according to an embodimentof the present invention.

FIG. 9 illustrates an example of an extended inclusion list, an extendedexclusion list and a substring information field format according to anembodiment of the present invention.

FIG. 10 illustrates another example of an extended inclusion list, anextended exclusion list, and a substring information field format.

FIG. 11 is a view illustrating an example of information included in thecapability filter information (CapabilityFilterInfo) element.

FIG. 12 illustrates an example of a filter preference field formatincluded in the capability filter information (CapabilityFilterInfo)element.

FIG. 13 illustrates an example of a security capability element fieldformat included in a capability filter information(CapabilityFilterInfo) element according to an embodiment of the presentinvention.

FIG. 14 illustrates another example of capability filter information(CapabilityFilterInfo) using an RSN information element according to anembodiment of the present invention.

FIG. 15 illustrates another example of a security capability elementfield format included in a capability filter information(CapabilityFilterInfo) element according to an embodiment of the presentinvention.

FIG. 16 illustrates another example of a security capability elementfield format included in a capability filter information(CapabilityFilterInfo) element according to an embodiment of the presentinvention.

FIG. 17 illustrates another example of the capability filter information(CapabilityFilterInfo) element according to an embodiment of the presentinvention.

FIG. 18 illustrates another example of capability filter information(CapabilityFilterInfo) according to an embodiment of the presentinvention.

FIG. 19 illustrates another example of capability filter information(CapabilityFilterInfo) according to an embodiment of the presentinvention.

FIG. 20 illustrates another example of a Filtering Preference fieldformat included in a capability filter information(CapabilityFilterInfo) element according to an embodiment of the presentinvention.

FIG. 21 illustrates an example of information included in an APoperating condition preference element according to an embodiment of thepresent invention.

FIG. 22 illustrates an example of information included in an AP networkpreference element according to an embodiment of the present invention.

FIG. 23 is a view illustrating an example of a Timeout Interval elementand a Probe Response listen start interval element according to anembodiment of the present invention.

FIG. 24 is a flow chart illustrating a process of performing activescanning by an STA that transmits a probe request frame according to anembodiment of the present invention.

FIG. 25 is a flow chart illustrating a process of performing activescanning by an AP which receives a probe request frame according to anembodiment of the present invention.

FIG. 26 is a block diagram of a wireless device to which an embodimentof the present invention is applicable.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, some embodiments of the present invention are described indetail with reference to the accompanying drawings in order for thoseskilled in the art to be able to readily implement the invention.Furthermore, the present invention is not limited to the followingembodiments and may be modified in various ways within the scope of thetechnical spirit of the present invention.

Elements described in this specification may include additional elementsother than elements to be described later, at need, and a detaileddescription of parts not directly related to the present invention orredundant parts is omitted. Furthermore, when it is said that any partincludes (or comprises) any element, it means the part does not excludeother elements and may further include other elements.

FIG. 1 is a view schematically illustrating an example of a wirelesslocal area network (WLAN) system to which an embodiment of the presentinvention is applicable.

Referring to FIG. 1, a WLAN system includes one or more basic servicesets (BSSs). A BSS refers to a set of stations (STAs) that cancommunicate with each other in synchronization, rather than a conceptindicating a particular area. A BSS may be classified into aninfrastructure BSS and an independent BSS (IBSS), and FIG. 1 illustratesan infrastructure BSS.

An infrastructure BSS (BSS1 and BSS2) may include one or more non-APstations (STA1, STA3, STA4), an access point (AP) providing adistribution service (DS), and a distribution system (DS) connecting aplurality of APs (AP1 and AP2). In the infrastructure BSS, the AP STAmay manage the non-AP STAs of the BSS.

Meanwhile, the IBSS is a BSS operating in an ad-hoc mode. The IBSS doesnot include an AP, so it cannot be a centralized management entityperforming a management function at the center. In the IBSS, every STAmay be configured as a mobile station, and the IBSS establishes aself-contained network, not allowing an access to a distribution system(DS).

A station (STA) is a certain functional medium including a medium accesscontrol (MAC) following the stipulation of the IEEE 802.11 standard anda physical layer interface with respect to a wireless medium. A stationincludes both AP and non-AP stations in a broad sense. A station forwireless communication may include a processor and a transceiver, andmay further include a user interface, a display unit, and the like. Theprocessor, a function unit devised to generate a frame to be transmittedvia a wireless network or process a frame received via the wirelessnetwork, performs various functions to control a station. Thetransceiver, which is functionally connected with the processor, isconfigured to transmit and receive frames via the wireless network forthe station.

Among the stations STAs, mobile terminal manipulated by a user arenon-AP STA (STA1, STA3, STA4, STA5). The non-AP STA may be referred toby other names such as terminal, wireless transmit/receive unit (WTRU),user equipment (UE), mobile station (MS), mobile terminal, mobilesubscriber unit, or the like.

The APs (AP1 and AP2) are functional entities for providing an access tothe DS by way of a wireless medium for an STA (Associated Station)associated thereto. In the infrastructure BSS including the APs, inprinciple, communications between non-AP STAs are made by way of theAPs, but when a direct link has been established (e.g., when a DLS orTDLS service is supported), the non-AP STAs can directly communicatewith each other. The AP may also be called by other names such ascentralized controller, base station (BS), node-B, base transceiversystem (BTS), site controller, and the like.

A plurality of infrastructure BSSs may be connected via the DS. Theplurality of BSSs connected via the DS is called an extended service set(ESS). STAs included in the ESS may communicate with each other, and anon-AP STA may move from one BSS to another BSS within the same ESSwhile seamlessly performing communication.

The DS is a mechanism allowing one AP to communicate with another AP.Through the DS, an AP may transmit a frame for STAs associated to theBSS managed by the AP, transfer a frame when one STA moves to anotherBSS, or transmit or receive frames to and from an external network suchas a wireline network. The DS may not be necessarily a network. Namely,the DS is not limited to any form so long as it can provide a certaindistribution service stipulated in the IEEE 802.11 standard. Forexample, the DS may be a wireless network such as a mesh network or aphysical structure connecting the APs.

FIGS. 2 and 3 are flow charts illustrating an active scanning method ina WLAN system. FIG. 2(a) is a flow chart illustrating a process ofperforming active scanning on one channel in the WLAN system, and FIG.2(b) is a flow chart illustrating a process of performing activescanning on a plurality of channels in the WLAN system.

Referring to FIGS. 2 and 3, when an STA wants to access a WLAN systemsuch as the ESS illustrated in FIG. 1, the STA transmits a probe requestframe to each channel of the WLAN system in a unicast manner or abroadcast manner. Here, the STA detects a state of one channel during aminimum channel time (MinChannelTime). Namely, the STA detects whetherthe channel is active or inactive. If the STA does not detect activityof one channel during the minimum channel time (channel 2, channel 4, orthe like, illustrated in FIG. 2(b)), the STA regards the channel asbeing inactive and scans another channel. Meanwhile, when the STAdetects activity of one channel within the minimum channel time, the STAwaits to receive (a) probe response frame(s) in the channel during maxchannel time (MaxChannelTime) which is longer than the minimum channeltime. When the maximum channel time is reached, the STA processes proberesponse frames received up to that time, and scans a next channel inthe same manner as described above. In this manner, the STA may selectan AP based on the scanning results with respect to respective channelsof the WLAN system.

As described above, in the existing active scanning method, when the STAbroadcasts the probe request frame to each channel, the STA generallydoes not have accurate information regarding a service set identifier(SSID), or the like, of an AP to which the STA wants to be connected,the STA uses a wild card SSID. Here, all the APs, which have receivedthe probe request frame from the STA, respond by a probe response frame,respectively, flooding of the probe response frames occurs.

Also, since the STA sequentially scans all the channels during apredetermined period of time regardless of particular informationincluded the probe response frames of the APs, a scanning time islengthened to result in a lengthened initial link setup time for the STAto be connected to the WLAN system. As illustrated in FIG. 2(b),although the STA discovers an AP appropriate to be associated accordingto the result of scanning of channel 1, the STA scans up to a finalchannel, so the scanning time may be lengthened more than necessary.

Meanwhile, when the AP receives the probe request frame from the STA,the AP unconditionally transmits a probe response frame withoutconsideration of whether to associate the corresponding STA, whether theSTA, which transmitted the probe request frame, is in a state of beingable to receive a probe response frame, and the like.

For example, as illustrated in FIG. 2(b), for example, in case that APssuch as AP 1-2, AP 1-3, AP 3-3, or the like, receive the probe requestframe from the STA not supporting capability requested by the APs,although the STA requests association to the APs such as AP 1-2, AP 1-3,and AP 3-3 afterwards, the APs will not permit association of the STAthereto, but the APs transmit a probe response frame to the STA. Such aprobe response frame is an unnecessary packet transmission, and althoughthe STA selects the APs and requests an association thereto, theassociation request will be rejected by the APs, so the probe responseframe causes delay in an association process.

Also, as illustrated in FIG. 3, when the APs unconditionally transmitprobe response frames to the STA without considering whether the STA,which has transmitted the probe request frame, is in a state of beingable to receive the probe response frames, flooding of the proberesponse frames may further caused. The STA, which has transmitted theprobe request frame, receives the probe response frames from the APsduring a maximum channel time in the corresponding channel, and when themaximum channel time has passed, the STA scans a next channel, so theSTA cannot receive a probe response frame transmitted via thecorresponding channel after the maximum channel time. However, in theexisting active scanning method, as mentioned above, the AP transmitsthe probe response frame without consideration of a state of the STAwhich has transmitted the probe request frame, and when the maximumchannel time has passed, the probe response frame is not received by theSTA which has transmitted the probe request frame. Since the proberesponse frame is transmitted in a unicast manner, if it is not receivedby the corresponding STA, the AP, which has transmitted the proberesponse frame, retransmits a probe response frame. Here, if the maximumchannel time has passed, the corresponding STA cannot receive theretransmitted probe response frame. Thus, the AP keeps transmitting ofthe probe response frame, causing serious frame response flooding.

Hereinafter, an effective active scanning method capable of reducingprobe response flooding and shortening a scanning time by solving theproblem of the existing active scanning method as described above willbe described.

FIGS. 4 and 5 are flow charts illustrating an active scanning method ina WLAN system according to an embodiment of the present invention. Theflow charts between the STA and the APs may be a procedure performedbetween a non-AP STA and APs constituting an infrastructure BSS, butobviously, the present invention is not limited thereto. For example,the present embodiment may be applied in the same or equal manner to anoperation between non-AP STAs constituting an IBSS, an operation betweenmesh points (MPs) constituting a mesh network system, and even anoperation between terminals or between a terminal and a base stationconstituting a different wireless communication system, except for acase which is not available in essence.

Referring to FIGS. 4 and 5, the STA transmits a probe request frameincluding a list indicating information regarding a response-target APvia a channel in a broadcast manner or a unicast manner (S400). Inresponse thereto, the STA receives probe response frames from an APbased on the list indicating information regarding the response targetAP included in the probe request frame (S410).

The list indicating information regarding the response target AP mayinclude information regarding a response target AP which is to respondto the probe request frame, and the list may be configured by using atleast one of an SSID (Service Set Identifier), a BSSID (Basic ServiceSet Identifier), an MESHID (Mesh Identifier), an HESSID (ExtendedService Set Identifier), and a network ID of a response target AP. Forexample, the list indicating information regarding a response target APmay be included in the probe request frame by using an inclusion list asdescribed hereinafter, and details thereof will be described later.

For example, as illustrated in FIG. 4, the STA may broadcast a proberequest frame including a list (e.g., an inclusion list) indicatinginformation regarding a response target AP via a channel 1. When an AP(e.g., AP 1-1, AP 1-2, . . . , AP 1-n), which has received the proberequest frame, corresponds to the list indicating information regardingthe response target AP included in the probe request frame, thecorresponding AP (e.g., AP1-1, etc.) may transmit a probe response frameto the STA.

Also, besides the list indicating information regarding the responsetarget AP as described above, the probe request frame may include a listindicating information regarding a response non-target AP which shouldnot respond to the probe request frame. For example, the list indicatinginformation regarding a response non-target AP may be included in theprobe request frame by using an exclusion list as described hereinafter,and the exclusion list may be configured by using at least one of anSSID (Service Set Identifier), a BSSID (Basic Service Set Identifier),an MESHID (Mesh Identifier), an HESSID (Extended Service SetIdentifier), and a network ID of a response non-target AP. Detailsthereof will be described later.

For example, as illustrated in FIG. 4, the STA may broadcast a proberequest frame including a list (e.g., an exclusion list) indicatinginformation regarding a response non-target AP via the channel 1. Whenan AP (e.g., AP 1-1, AP 1-2, . . . , AP 1-n), which has received theprobe request frame, corresponds to the list indicating informationregarding a response non-target AP included in the probe request frame,the corresponding AP does not transmit a probe response frame to theSTA.

As described above, the probe request frame according to an embodimentof the present invention may include one of the list indicatinginformation regarding a response target AP and the list indicatinginformation regarding a response non-target AP, and may include both thelist indicating information regarding a response target AP and the listindicating information regarding a response non-target AP and may betransmitted.

The probe request frame according to an embodiment of the presentinvention may include capability information regarding a station orpreference information regarding a response target AP, as well as thelist (e.g., an inclusion list) indicating information regarding aresponse target AP and the list (e.g., an exclusion list) indicatinginformation regarding a response non-target AP as described above.

The capability information regarding a station may include at least oneof extended capability information regarding a station, high throughput(HT) capability information, very high throughput (VHT) capabilityinformation, and security capability information. The preferenceinformation regarding a response target AP may include at least one ofsecurity preference information regarding a response target AP,capability preference information regarding a response target AP,Internet access preference information, operating condition preferenceinformation regarding a response target AP, and network preferenceinformation.

Referring to FIG. 4, the STA transmits a probe request frame includingat least one of capability information regarding a station andpreference information regarding a response target AP via a channel(S420). In response thereto, the STA receives a probe response framefrom the AP satisfying the information (capability information regardinga station or preference information regarding a response target AP)included in the probe request frame (S430). Based on the capabilityinformation regarding a station and the preference information regardinga response target AP, when the AP, which has received the probe requestframe, receives an association request from the STA afterwards, it maynot permit an association of the STA, or if capability of the station orpreference regarding a response target AP is not satisfied, the AP maynot transmit a probe response frame to the STA or transmit a null proberesponse frame to the STA (S435).

For example, the STA may transmit a probe request frame includingcapability information regarding a station or preference informationregarding a response target AP via a channel 3. Upon receiving the proberequest frame, when the AP (e.g., AP 3-1, AP 3-2, . . . , AP 3-n)satisfies the capability information regarding a station and thepreference information regarding a response target AP based on theinformation included in the probe request frame, the AP may transmit aprobe response frame to the STA. If the AP (e.g., AP 3-1, AP 3-2, . . ., AP 3-n), which has received the probe request frame, receives anassociation request from the STA afterwards and the AP will not permitan association of the STA because the capability of the STA is notsufficient, the AP may not transmit a probe response frame or maytransmit a null probe response frame to indicate that the STA cannot beassociated. Also, when the AP, which has received the probe requestframe, cannot satisfy preference of the STA, namely, preference withrespect to a response target AP, the AP may not transmit a proberesponse frame or may transmit a null probe response frame to indicatethat the STA cannot be associated.

Meanwhile, in the case of the existing active scanning method, the STAshould sequentially perform scanning on every channel unconditionally upto a predetermined time, the scanning time may be lengthened more thannecessary.

However, in the case of the active scanning method according to anembodiment of the present invention, as illustrated in FIG. 4, the STAgenerates an intermediate scanning result during scanning and returnsit, and when an AP appropriate to be associated is discovered from theintermediate scanning result, the STA may instruct scanning abort(S440). Thus, when the STA discovers an appropriate AP, it may performscanning abort during scanning, shortening a scanning time.

For example, a service primitive such as “MLME-SCAN-ABORT.request( )”may be included in the IEEE 802.11 standard. The active scanning processperformed by the STA may be aborted by using the service primitive.Also, by extending a “MLME-SCAN.confirm( )” service primitive, anintermediate scanning result may be returned during active scanning toallow the STA to check APs discovered up to a particular timing. Evenafter the STA instructs scanning abort during active scanning,information regarding an AP discovered up to the abort timing isreturned. Here, when the STA receives a null probe response frame, the“MLME-SCAN.confirm( )” service primitive may transfer the informationtogether, and if a response code is received together, the“MLME-SCAN.confirm( )” service primitive may also transfer theparticulars so that MESHID, BSSID, or the like, of the AP (or STA) whichhas transmitted the null probe response frame may be removed from theinclusion list and may be included in the exclusion list so as to beexcluded from probe response targets in a next scanning session. When anappropriate AP is discovered from the intermediate scanning resultreturned during the active scanning as described above, the STA mayinstruct scanning abort and select an AP to be associated by using APinformation discovered up to the abort timing.

Also, in the active scanning method according to an embodiment of thepresent invention, a selective scanning method whereby a channel havinga high likelihood of having an AP is preferentially scanned to rapidlydiscover an appropriate AP is provided.

Referring to FIG. 4, the STA selects a next channel to be scanned basedon the information included in the received probe response frame. Theprobe response frame may include neighbor AP information such as an APchannel report element, a neighbor report element, or the like. The APchannel report element is an element defined in the IEEE 802.11ktechnology, which includes a list of channels in which the STA has highprobability of discovering an AP.

For example, after the STA transmits a probe request frame with respectto a first channel at an initial stage of active scanning, if a proberesponse frame received from an AP includes an AP channel reportelement, a neighbor report element, or the like, the channels reportedto be included in the element have a high probability of having APs.Thus, when the STA selects a channel to be scanned next from the list ofchannels on which the STA performs active scanning, the STApreferentially selects a channel included in the AP channel reportelement or a neighbor report element. Also, the STA checks an AP channelreport element of a probe response frame received via scanned channeleach time, and first scans a channel (i.e., a channel on the channellist undergoing active scanning, which has not been scanned yet) amongchannels included therein. Namely, the STA preferentially uses channelinformation of an AP channel report element included in the mostrecently received probe response frame. When a channel to be selectivelyscanned is selected, an appropriate AP can be more quickly discovered,and when an appropriate AP is discovered, scanning abort may beinstructed to abort scanning.

Also, a field for inferring a channel around an AP, locationinformation, and the like, as well as a neighbor report element, may beincluded in a probe response frame and transmitted. The neighbor reportelement includes a BSSID, capability, channel information with respectto a neighbor AP present in the vicinity of an AP which has transmitteda probe response frame. A channel to be selectively scanned may beselected based on the information regarding the neighbor AP such as theneighbor report element, or the like. Also, based on informationincluded in information regarding a neighbor AP received in a proberesponse frame such as a neighbor report element, or the like, when theSTA determines that the AP satisfies capability with respect to astation or preference with respect to a response target AP as describeabove, the STA may immediately request association from thecorresponding AP.

Also, the STA may first selectively perform scanning on a channel havingan AP in a position near the STA with reference to location relatedinformation such as a location parameter element, a measurement reportelement, or the like.

As described above, in an additional method besides the selectivescanning using a probe response frame, in case of using 2.4 GHz, achannel which is frequently used in general may be preferentiallyscanned. For example, in a 2.4 GHz WLAN, channels 1, 6, and 11 are mostfrequently used, so the channels 1, 6, and 11 may be preferentiallyscanned.

In another additional method, a short beacon such as a measurement pilotframe may be used. The measurement pilot frame is smaller than a beaconand frequently transmitted. Although the STA is in the course of activescanning, if it receives the measurement pilot frame, the STA maypreferably scans the channel because an AP surely exists in the channelincluded in the measurement pilot frame. Or, since the measurement pilotframe includes information regarding an BSSID and basic informationregarding an AP, if the STA determines that it can be associated withthe corresponding AP based on the information, the STA may abort thecurrently performed scanning at an early stage through a scanning abortinstruction. If the information included in the measurement pilot frameis not sufficient for the STA to determine whether to be associated withan AP, the STA may wait for a beacon frame transmitted from the AP whichhas transmitted the measurement pilot frame immediately after themeasurement pilot frame is received, to additionally search forinformation included in the beacon frame, and perform association basedon the searched information.

Also, a duration up to a next full beacon or a broadcast probe responseframe may be indicated in a measurement pilot frame, other short beacontype information, or a short probe response frame. Here, when the STArequires additional information, it may await till the indicatedduration and request additional information required for an associationfrom a full beacon or a broadcast probe response frame. Since the STAmay accurately know duration information up to a next full beacon or abroadcast probe response frame, it may be in power save mode in theduration.

Also, the STA may refer to a probe response frame requested by adifferent STA. In particular, in case that a different STA transmits aprobe request frame in a broadcast manner, when a probe response frameis received in response thereto, the STA may obtain informationregarding an AP with reference to information included in the receivedprobe response frame. The STA may immediately be associated with thecorresponding AP if it is possible based on the obtained informationregarding the AP or may transmit a probe request frame to thecorresponding AP in a unicast manner to more quickly perform scanning.

As described above, when the selective scanning method according to anembodiment of the present invention is used in association with theforegoing scanning abort function, a scanning time can be remarkablyreduced.

Meanwhile, a probe request frame according to an embodiment of thepresent invention may include information regarding a response receptiontime.

The information regarding response reception time may includeinformation indicating a duration in which a station may receive a proberesponse frame as a response to the probe request frame on one channel.For example, the information regarding a response reception time may beincluded in a probe request frame by using a timeout intervalinformation element or a probe response deadline interval informationelement indicating a duration in which a probe response frame may bereceived, and details thereof will be described later.

Referring to FIG. 5, the STA transmits a probe request frame includinginformation regarding a response reception time, i.e., information(e.g., a timeout interval element) indicating a duration in which theprobe response frame may be received, via a channel (S500). Uponreceiving it, an AP (or a mesh STA, an STA of IBSS) checks informationregarding a response reception time (e.g., a timeout interval element),and when it is a duration in which a probe response frame may bereceived, the AP transmits a probe response frame (S510). Meanwhile,when the duration in which the probe response frame may be received haspassed, the AP does not transmit a probe response frame (S520).

According to an embodiment of the present invention, the STA clarifies aduration in which the STA, which transmits a probe request frame, may beable to actually receive a probe response frame, in the probe requestframe, so that APs may transmit a probe response frame only in thecorresponding duration. Thereafter, when the duration clarified in theprobe request frame, i.e., the duration in which the probe responseframe may be received has lapsed, since the APs do not transmit proberesponse frames, flooding of probe response frames as mentioned abovedoes not occur.

The existing minimum channel time and maximum channel time aredetermined by the STA which transmits the probe request frame, but theinformation on them are not transmitted to the AP (or STA) whichreceives the probe request frame. Thus, in an embodiment of the presentinvention, the STA, which transmits a probe request frame, determines aduration (e.g., a timeout interval) in which it may receive a proberesponse frame in consideration of its minimum channel time and amaximum channel time, and includes the determined duration in a proberequest frame, and the duration is transmitted to the APs (or STAs). Forexample, the timeout interval may be determined as expressed by Equation1 shown below.MinChannelTime<=Timeout Interval<=MaxChannelTime  [Equation 1]

Here, when an AP (or STA) receives a probe request frame includinginformation regarding a duration (e.g., a timeout interval) in which aprobe response frame may be received as determined by Equation 1, ittransmits a probe response frame to the STA from a timing at which theprobe request frame is received to a timing at which the probe responseframe reception-available duration (e.g., the timeout interval) has notlapsed, and when the duration has passed, the AP does not transmit aprobe response frame. Also, in the case that the AP retransmits a proberesponse frame, the AP retransmits the probe response frame up to atiming at which the probe response frame reception available duration(e.g., the timeout interval) has not lapsed, and when the timeoutinterval has lapsed, the AP does not retransmit a probe response frame.

In general, when the STA transmits a probe request frame, it listens toa corresponding channel immediately after the probe request frame istransmitted. However, in some cases, the STA may want to receive a proberesponse frame by starting listening with some delay, rather thanimmediately receiving a probe response frame. In this case, the proberequest frame may further include information indicating a time at whichthe STA starts to receive a probe response frame in the probe requestframe, in addition to the information indicating the probe responseframe reception available duration (e.g., the timeout interval). Forexample, the information indicating a time at which a probe responseframe starts to be received may be included in a probe request frame byusing a probe response listen start interval element, and detailsthereof will be described later.

For example, when only the information indicating the probe responseframe reception available duration (e.g., the timeout interval) isincluded in the probe request frame and transmitted, the STA, which hastransmitted the probe request frame, receives a probe response frame inthe probe response frame reception available duration immediately afterthe probe request frame is transmitted, and the AP may transmit a proberesponse frame only in the probe response frame reception availableduration (e.g., the timeout interval).

Meanwhile, when information indicating a time at which a probe responseframe starts to be received together with information indicating theprobe response frame reception available duration is included in a proberequest frame and transmitted, the STA, which has transmitted the proberequest frame, starts to listen to a probe response frame starting froma timing at which a probe response frames starts to be received asindicated in the probe request frame (e.g., a probe response listenstart interval) after transmitting the probe request frame. The STAreceives a probe response frame in the probe response frame receptionavailable duration (e.g., the timeout interval) from a timing at whichlistening starts, and the AP transmits a probe response frame in theprobe response frame reception available duration (e.g., the timeoutinterval) starting from a timing indicated by the time in the proberequest frame at which a probe response frame starts to be received(e.g., the probe response listen start interval). The AP does nottransmit a probe response frame before the time at which a proberesponse frames starts to be received indicated in the probe requestframe. (e.g., the probe response listen start interval).

FIG. 6 illustrates an example of information items included in aninclusion list according to an embodiment of the present invention.

The inclusion list includes information regarding a response target APwhich is to respond to the probe request frame as described above.Namely, the inclusion list may include at least one of an SSID (ServiceSet Identifier), a BSSID (Basic Service Set Identifier), an MESHID (MeshIdentifier), an HESSID (Extended Service Set Identifier), and a networkID of an AP (or an STA) which is to respond to the probe request frame.

The inclusion list may be used by defining an information element, andit is merely an example and may be included in the form of a subfield ina probe request frame. Alternatively, the inclusion list may be includedin the form of a subfield in a third information element or field, andthe corresponding information element or field may be included in aprobe request frame. In the description of the present disclosure, theorder of the respective fields of a length thereof is merelyillustrative and may be appropriately modified to be used, and somefields may be added or deleted as necessary.

As illustrated in FIG. 6(a), an inclusion list element 610 may includeElement ID indicating an element identification value, Length indicatinga length of the inclusion list, BSSID List indicating a list of BSSIDelements with respect to BSSs which should transmit a response withrespect to a probe request frame, MESHID List indicating a list ofMESHID elements with respect to mesh STAs which should transmit aresponse with respect to a probe request frame, HESSID List indicating alist of HESSID elements with respect to STAs which should transmit aresponse with respect to a probe request frame, and other Networkidentifier List indicating a network identification value.

Here, the Length field may be a value indicating a length of theinclusion list by octet, and the length may be variable. The OtherNetwork identifier List field may be a list of values identifyingnetworks such as a roaming consortium organization identifier, a roamingconsortium element, or the like, defined in the IEEE 802.11u technology.For example, a roaming consortium element including informationregarding a roaming consortium to which an STA has joined may be definedas illustrated in FIG. 6(b) so as to be used.

Referring to FIG. 6(b), the roaming consortium element 620 may includeNumber of ANQP OIs indicating a number of roaming consortium OI(Organization Identifier), OI #1 and #2 Lengths indicating a length ofOI (Organization Identifier), and OI #1, OI #2 and OI #3 indicating anID of a roaming consortium.

Here, when a single roaming consortium is designated, only one OI(Organization Identifier), rather than information element form asillustrated in FIG. 6(b), may be included in an inclusion list or anexclusion list, and a plurality of OI (Organization Identifier) may beincluded in the form of a subfield, rather than in the form of aninformation element, in the inclusion list or exclusion list.

Also, as illustrated in FIG. 6(c), the inclusion list element 630 mayfurther include an SSID List field. In this case, the inclusion listelement 630 is the same as the format of the exclusion list. The APs (orSTAs) included in the existing SSID List may be included in the SSIDList of the inclusion list element 630, or the APs (or STAs) included inthe existing SSID List may not be used and only the APs (or STAs)included in the SSLID List of the inclusion list element 630 accordingto an embodiment of the present invention may be used.

FIG. 7 is a view illustrating an example of information items includedin an exclusion list according to an embodiment of the presentinvention.

The exclusion list includes information regarding a response non-targetAP which should not respond to a probe request frame as described above.Namely, the exclusion list includes at least one of an SSID (Service SetIdentifier), a BSSID (Basic Service Set Identifier), an MESHID (MeshIdentifier), an HESSID (Extended Service Set Identifier), and a networkID of a response non-target AP (or STA) which should not respond to aprobe request frame.

The exclusion list may be used by defining an information element, andit is merely an example and may be included in the form of a subfield ina probe request frame. Alternatively, the inclusion list may be includedin the form of a subfield in a third information element or field, andthe corresponding information element or field may be included in aprobe request frame. In the description of the present disclosure, theorder of the respective fields of a length thereof is merelyillustrative and may be appropriately modified to be used, and somefields may be added or deleted as necessary.

Referring to FIG. 7, an exclusion list element 710 may include ElementID indicating an element identification value, Length indicating alength of the exclusion list, SSID List indicating a list of SSIDelements with respect to STAs which should not transmit a response withrespect to a probe request frame, BSSID List indicating a list of BSSIDelements with respect to BSSs which should not transmit a response withrespect to a probe request frame, MESHID List indicating a list ofMESHID elements with respect to mesh STAs which should not transmit aresponse with respect to a probe request frame, HESSID List indicating alist of HESSID elements with respect to STAs which should not transmit aresponse with respect to a probe request frame, and other Networkidentifier List indicating a network identification value.

Here, the Length field may be a value indicating a length of theexclusion list by octet, and the length may be variable. The OtherNetwork identifier List field indicating a network identification valuemay be a list of values identifying networks such as a roamingconsortium organization identifier, a roaming consortium element, or thelike, defined in the IEEE 802.11u technology. In the above, the roamingconsortium element including information regarding a roaming consortiumthe STA has joined has been described with reference to FIG. 6(b)according to an embodiment of the present invention.

Meanwhile, an existing “MLME-SCAN.request” service primitive may extendas shown in Table 1 to reflect the foregoing inclusion list andexclusion list.

TABLE 1 MLME-SCAN.request ( BSSType, BSSID, SSID, ScanType, ProbeDelay,ChannelList, MinChannelTime, MaxChannelTime, RequestInformation, SSIDList, ChannelUsage, AccessNetworkType, HESSID, MeshID, Inclusion List,Exclusion List, CapabilityFilterInfo, VendorSpecificInfo )

FIG. 8 is a view illustrating formats of information elements includedin the inclusion list or the exclusion list according to an embodimentof the present invention.

Referring to FIG. 8(a), a BSSID element 810 may include Element IDindicating an element identification value, Length indicating a lengthof a BSSID, and BSSID indicating a BSSID or a MAC address of a STA.

Here, the Length field may be a value indicating a length of a BSSID byoctet. When all the BSSID fields are 1, it may indicate a wildcardBSSID.

The BSSID element 810 may be included in a form of an informationelement in the inclusion list or the exclusion list, or may be includedin a form of a field in which BSSID information is arranged, rather thanan information element form, in the inclusion list or exclusion list.

Referring to FIG. 8(b), an HESSID element 820 may include Element IDindicating an element identification value, Length indicating a lengthof a HESSID, and HESSID indicating a HESSID.

Here, the Length field may be a value indicating a length of an HESSIDby octet. When all the HESSID fields are 1, it may indicate a wildcardHESSID.

The HESSID element 820 may be included in a form of an informationelement in the inclusion list or the exclusion list, or may be includedin a form of a field in which HESSID information is arranged, ratherthan an information element form, in the inclusion list or exclusionlist.

Referring to FIG. 8(c), a BSSID element 830 may include Element IDindicating an element identification value, Length indicating a lengthof a BSSID List, and BSSID List indicating a list of BSSID elementscorresponding to respective BSSIDs whose information is requested by anSTA.

Here, the Length field may be a value indicating a length of BSSID Listby octet, and the length may be variable. The BSSID List field may be alist of BSSID elements 810 illustrated in FIG. 8(a). When a value of theLength field is 0, the BSSID List field may indicate a wildcard BSSID.

The BSSID List element 830 may be included in a form of an informationelement in the inclusion list or the exclusion list, or may be includedin a form of a field in which BSSID List information is arranged, ratherthan an information element form, in the inclusion list or exclusionlist.

Referring to FIG. 8(d), an HESSID element 840 may include Element IDindicating an element identification value, Length indicating a lengthof an HESSID List, and HESSID List indicating a list of HESSID elementscorresponding to respective HESSIDs whose information is requested by anSTA.

Here, the Length field may be a value indicating a length of HESSID Listby octet, and the length may be variable. The HESSID List field may be alist of HESSID elements 810 illustrated in FIG. 8(b).

The HESSID List element 840 may be included in a form of an informationelement in the inclusion list or the exclusion list, or may be includedin a form of a field in which HESSID List information is arranged,rather than an information element form, in the inclusion list orexclusion list.

Referring to FIG. 8(e), an MESHID element 850 may include Element IDindicating an element identification value, Length indicating a lengthof an MESHID List, and MESHID List indicating a list of MESHID elementscorresponding to respective MESHIDs whose information is requested by anSTA.

Here, the Length field may be a value indicating a length of MESHID Listby octet, and the length may be variable. The MESHID List field may be alist of HESSID elements including Element ID, Length, and MESHID.

The MESHID List element 850 may be included in a form of an informationelement in the inclusion list or the exclusion list, or may be includedin a form of a field in which MESHID List information is arranged,rather than an information element form, in the inclusion list orexclusion list.

Meanwhile, as described above, a set of response target APs (or STAs)may be limited more minutely by using the inclusion list including atleast one of BSSID, SSID, SSID List, HESSID, MESHID, Network ID, andNetwork ID List of an AP which should respond to a probe request frame.

For example, a condition for minutely confining a set of a responsetarget APs (or STAs) together with the BSSID, SSID, SSID List, HESSID,MESHID, Network ID, and Network ID List information in the inclusionlist.

Alternatively, a response target AP (or STA) may be designated by BSSID,SSID, SSID List, HESSID, MESHID, Network ID, Network ID List included inthe Inclusion List, without using BSSID, SSID, HESSID, MESHID, and thelike, defined in the existing standard. In this case, the BSSID, SSID,HESSID, MESHID, and the like, defined in the existing standard is notincluded in a probe request frame. For example, the BSSID may not beincluded in a probe request frame, or a MAC address of an STAtransmitting a probe request frame may be included in a probe requestframe such that any AP (or STA) may not respond to the probe requestframe, or an unused MAC address such as 000 . . . 00, 111 . . . 11, orthe like, may be included in a probe request frame. An SSID may not beincluded in a probe request frame, or an unused SSID value such as anull string, or the like, may be included in a probe request frame sothat any AP (or STA) may not respond to a probe request frame. In thiscase, no target is designated in an existing ID (identifier) and aresponse target AP (or STA) indicated in the inclusion list isdesignated.

Alternatively, a set of response target APs (or STAs) may be minutelyconfined by using the sum of sets of a set of APs (or STAs) designatedin the BSSID, SSID, HESSID, MESHID, and the like, defined in theexisting standard and a set of response target APs (or STAs) designatedin the inclusion list.

Also, as described above, a set of APs (or STAs) which should notrespond may be minutely confined by using an exclusion list including atleast one of BSSID, SSID, SSID List, HESSID, MESHID, Network ID, andNetwork ID List of an AP which should not responds to a probe requestframe. For example, a condition for minutely confining a set of APs (orSTAs) which should not respond may be designated together with theBSSID, SSID, SSID List, HESSID, MESHID, Network ID, and Network ID Listinformation in the exclusion list.

Alternatively, a response target AP (or STA) or APs (or STAs) whichshould not respond may be confined by using a set of response target APs(or STAs) designated in the inclusion list and a set of APs (or STAs)which should not respond as designated in the exclusion list together.For example, a set of APs (or STAs) which should not respond asdesignated in the exclusion list may be excluded from the set ofresponse target APs (or STAs) designated in the inclusion list, or aresponse target AP (or STA) additionally designated in the inclusionlist may be added in the set of response target APs (or STAs) designatedby applying even the exclusion list.

The probe request frame according to an embodiment of the presentinvention may include an inclusion list and an exclusion list or may notinclude them. Alternately, the probe request frame according to anembodiment of the present invention may include only one of theinclusion list and the exclusion list. The same BSSID, SSID, SSID List,HESSID, MESHID, Network ID, and Network ID List may not be included inboth the inclusion list and the exclusion list. A legacy AP (or STA) notsupporting the active scanning method according to an embodiment of thepresent invention cannot interpret an information element with respectto the inclusion list and the exclusion list, so although the inclusionlist and the exclusion list are included in the probe request frame, thelegacy AP (or STA) disregards it and may transmit a probe response frameaccording to an existing active scanning procedure.

Meanwhile the BSSID, SSID, HESSID, MESHID, and Network ID included inthe inclusion list and the exclusion list may use a full BSSID, SSID,HESSID, MESHID, and Network ID, or may use only a portion (substring) ofa full ID.

Hereinafter, a method of supporting a substring using only a portion ofBSSID, SSID, HESSID, MESHID, and Network ID information included in theinclusion list or the exclusion list will be described.

According to a first method, whether a substring is used may beindicated in a capability field of an extended capabilities element. Inorder to indicate whether an ID (e.g., BSSID, SSID, HESSID, MESHID,Network ID) included in the inclusion list or the exclusion list is afull ID or a partially included substring, a capability field of theexisting IEEE 802.11 standard may extend as shown in Table 2 below andused.

TABLE 2 Bit Information Notes . . . . . . . . . Xx Substring is used ininclusion When SSID or MESHID uses a list/exclusion list. substring ininclusion list/exclusion list, it is set as 1, otherwise, it is set as0. X x-n Reserved

In such a case, the inclusion list may use a format additionallyincluding SSID List as illustrated in FIG. 6(c).

As shown in Table 1, when the SSID or MESHID included in the inclusionlist or exclusion list indicates a full ID, “Xx” bit is set as 0, andwhen the SSID or MESHID indicates a substring, “Xx” bit is set as 1. Ifthe SSID or MESHID indicates a substring, the SSID or MESHID included inthe inclusion list or the exclusion list includes the substring andevery SSID or MESHID contains the indicated substring is matched. Forexample, when a substring “SKT” is included in an SSID included in theinclusion list, it may be handled in the same manner as an SSID such asSKT-abcd, SKT-1234 is included in the inclusion list.

In case of introducing a new capability field for a fast link setup, abit such as “Xx” of Table 1 may be added to the newly introducedcapability field and whether to use a substring may be indicated in asimilar manner, without extending the existing capability field asmentioned above.

According to a second method, a substring information (SubstringInfo)field indicating whether to use a substring is added to an inclusionlist or an exclusion list.

To this end, as illustrated in FIG. 9, an extended inclusion list or anextended exclusion list obtained by adding a substring information fieldto the inclusion list or the exclusion list may be used.

FIG. 9 illustrates an example of an extended inclusion list, an extendedexclusion list and a substring information field format according to anembodiment of the present invention.

Referring to FIG. 9(a), the extended inclusion list 910 includes aSubstringInfo field indicating whether a substring is used. The otherremaining fields are the same as those of the inclusion list illustratedin FIG. 6(c).

Referring to FIG. 9(b), the extended exclusion list 920 includesSubstringInfo field indicating whether a substring is used. The otherremaining fields are the same as those of the exclusion list illustratedin FIG. 7.

Here, the SubstringInfo field included in the extended inclusion list910 and the extended exclusion list 920 may be configured as the formatillustrated in FIG. 9(c).

Referring to FIG. 9(c), the SubstringInfo field 930 includes SubstringSupported indicating whether an STA uses an SSID or MESHID as asubstring, and Substring Type indicating a type of a substring includedin the SSID or MESHID.

For example, when a value of the Substring Supported field is 1, it mayindicate that a corresponding STA uses the SSID or MESHID as asubstring, and when a value of the Substring Supported field is 0, itmay indicate that the corresponding STA does not use the SSID or MESHIDas a substring. In this case, a value of the Substring Type field may be“reserved”.

Table 3 below shows a substring type according to a value of theSubstring Type field. This is merely illustrative, and the value of theSubstring Type field may be changeable.

TABLE 3 Value Meaning 0 A string used in an SSID or Mesh ID elementincluded in an exclusion list or an inclusion list is an actual SSID orMesh ID (Namely, a string indicated in a corresponding element is anactual SSID or Mesh ID, rather than a substring). 1 A string used in anSSID or Mesh ID element included in an exclusion list or an inclusionlist is a substring of an actual SSID or Mesh ID. An actual SSID or MeshID corresponding to an STA as a probe request target is an SSID or aMesh ID starting or ending with a substring included in an SSID or MeshID element included in an exclusion list or an inclusion list, orincluding the substring included in an SSID or Mesh ID element includedin an exclusion list or an inclusion list. 2 A string used in an SSID orMesh ID element included in an exclusion list or an inclusion list is asubstring of an actual SSID or Mesh ID. An actual SSID or Mesh IDcorresponding to an STA as a probe request target is a Mesh ID startingwith a substring included in an SSID or Mesh ID element included in anexclusion list or an inclusion list. 3 A string used in an SSID or MeshID element included in an exclusion list or an inclusion list is asubstring of an actual SSID or Mesh ID. An actual SSID or Mesh IDcorresponding to an STA as a probe request target is a Mesh ID endingwith a substring included in an SSID or Mesh ID element included in anexclusion list or an inclusion list. 4-7 Reserved

By using the substring information (SubstringInfo) field as shown inTable 1, whether MESHID or SSID included in the inclusion list orexclusion list is a substring may be indicated, and whether a substringis used is indicated all at once with respect to all the MESHIDs orSSIDs included in the inclusion list or the exclusion list. Namely, withrespect to an individual MESHID or SSID, a substring form may not bedifferently designated but the entirety may be designated by the sameoption. For example, according to a result of checking a substringinformation field in the inclusion list or the exclusion list includedin a probe request frame, if a substring has been used, every SSID orMESHID using the SSID or MESHID included in the inclusion list or theexclusion list, as a substring is matched.

According to a third method, a substring information (SubstringInfo)field indicating whether a substring is used in the inclusion list orthe exclusion list is added. In this method, the foregoing second methodis modified such that whether to use a substring may be indicated byusing a substring information field with respect to each of the MESHIDand SSID.

To this end, as illustrated in FIG. 10, an extended inclusion list or anextended exclusion list may be used.

FIG. 10 illustrates another example of an extended inclusion list, anextended exclusion list, and a substring information field format.

FIG. 10(a) shows another example of the extended inclusion list 1010,and FIG. 10(b) is another example of the extended exclusion list 1020.Here, in the extended inclusion list 1010 and the extended exclusionlist 1020, the other elements, excluding Extended SSID List and ExtendedMESHID List elements, are the same as those of the inclusion listillustrated in FIG. 6(c) and the exclusion list illustrated in FIG. 7.The Extended SSID List element is as shown in FIG. 10(c), and theExtended MESHID List element may be configured as shown in FIG. 10(d).

Referring to FIG. 10(c), the Extended SSID List element 1030 includes anSSID included in an inclusion list or an exclusion list and aSubstringInfo field indicating whether to use a substring with respectto the SSID, as a pair. Thus, whether to use a substring, or a usageform of a substring may be differently designated for each SSID.

Namely, a pair of SubstringInfo field indicating whether to use asubstring with respect to one SSID and a corresponding SSID field isincluded in the Extended SSID List element 1030 iteratively by an amountof SSIDs included in the inclusion list or the exclusion list. Throughthis, substrings may be used in different forms with respect to eachSSID. Here, in a pair of the SubstringInfo field and the SSID field, theSSID may be used in one of the following two forms.

(i) An SSID field having a 32-octet length is used and a string isincluded in an SSID field

(ii) An SSID element defined in an existing IEEE 802.11 standard is usedand a string is included in an SSID field of an SSID element.

An SSID included in a single inclusion list or exclusion list may beused in one of the two forms, and the two forms may not be mixed to beused.

Referring to FIG. 10(d), an Extended MESHID List element 1040 includesMESHID included in an inclusion list or an exclusion list and aSubstringInfo field indicating whether to use a substring with respectto the MESHID, as a pair. Thus, whether to use a substring, or a usageform of a substring may be differently designated for each MESHID.

Namely, a pair of SubstringInfo field indicating whether to use asubstring with respect to one MESHID and a corresponding MESHID field isincluded in the Extended MESHID List element 1040 iteratively by anamount of MESHIDs included in the inclusion list or the exclusion list.Through this, substrings may be used in different forms with respect toeach MESHID. Here, in a pair of the SubstringInfo field and the MESHIDfield, the MESHID may be used in one of the following two forms.

(i) An MESHID field having a 32-octet length is used and a string isincluded in an MESHID field

(ii) An MESHID element defined in the existing IEEE 802.11 standard isused and a string is included in an MESHID field of an MESHID element.

An MESHID included in a single inclusion list or exclusion list may beused in one of the two forms, and the two forms may not be mixed to beused.

As described above, when a substring is used in each SSID or MESHIDaccording to results of checking each SubstringInfo field of ExtendedSSID List, Extended MESHID List in the inclusion list or exclusion listincluded in the probe request frame, every SSID or MESHID using eachSSID or each MESHID included in the inclusion list or the exclusion listas a substring is matched.

Also, the SubstringInfo field included in the foregoing Extended SSIDList element 1030 and the Extended MESHID List element 1040 is the sameas that described above with reference to FIG. 9(c).

Hereinafter, the capability information regarding a station andpreference information regarding a response target AP included in aprobe request frame according to an embodiment of the present inventionwill be described in detail.

An AP receives a probe request frame, and when capability of an STAwhich has transmitted the probe request frame is not sufficient, the APmay not transmit a probe response frame. Or, the AP may transmit a nullprobe response frame indicating that the STA cannot be associated, tothe STA. The AP may determine whether the STA can be associated based onthe capability information regarding the station included in the proberequest frame, and transmit a probe response frame or a null proberesponse frame.

Also, when the AP, which has received the probe request frame, does notsatisfy preference information regarding an AP included in the proberequest frame, the AP may not transmit a probe response frame or maytransmit a null probe response frame.

For example, when the AP receives the probe request frame, it may checkcapability information of the station, e.g., extended capabilityinformation, high throughput (HT) capability information, very highthroughput (VHT) capability information, and the like, from the proberequest frame, and recognize capability of the STA such as whether theSTA is a 802.11n STA or 802.11ac STA, how wide of bandwidth the STA cansupport, and the like. Based on the information, the AP may determinewhether to transmit a probe response frame.

Also, when the AP receives the probe request frame, it may checkpreference information from the STA regarding an AP, for example,requirements by the requesting STA regarding an AP such that a securitypreference by the STA whether the STA desires not to use securityfunction such as ciphering, or the like although the function isprovided by the STA, preference on whether the STA only wants to use HTor VHT AP, preference on whether an Internet access is desired,preference on AP operation condition required by the STA including anaccess delay of an AP, or an available current admission capacity, andthe like, requirements with respect to AP resource such as a bandwidthof an AP, spatial stream utilization, or the like, preference of anadvertisement protocol supported by an AP, an access network typepreferred by the STA, preference such as venue information in which theAP is located, and the like, from the probe request frame, determinewhether the AP may be able to satisfy the conditions with respect to thepreference of the STA, and determine whether to transmit a proberesponse frame based on the determination.

The elements included in the capability information regarding thestation and the preference information regarding the response target APare merely illustrative and the respective elements may be changed intovarious formats so as to be used, and order, length, and the like, ofthe elements may be modified as necessary. Also, some of the elementsincluded in the capability information regarding the station and thepreference information regarding the response target AP may beselectively used and other elements may be added to be extended.

The capability information regarding the station according to anembodiment of the present invention may be included in the probe requestframe by using an RSN (Robust Security Network) information element.

The RSN information element, defined in the existing 802.11, includesinformation regarding a ciphering algorithm supported by the STA, anauthentication method, security capability, and the like. The AP mayrecognize security processing capability of the STA based on theelement. If the STA supports a security option such as a particularciphering algorithm but does not want to use it, the STA may not includea security parameter such as a corresponding algorithm, or the like, inthe RSN information element. Here, PKMID-Count, PKMID List, or the like,among the existing RSN information elements that indicate capability,may not be included since they are not essential for indicating thecapability.

Or, the capability information regarding the station and the preferenceinformation regarding the response target AP according to an embodimentof the present invention may be included in a probe request frame bydefining a capability filter information (CapabilityFilterInfo) element.

FIG. 11 is a view illustrating an example of information included in thecapability filter information (CapabilityFilterInfo) element. Thecapability filter information (CapabilityFilterInfo) element is includedin a probe request frame, and allows the AP (or STA), which has receivedthe probe request frame, to recognize capability and preference of theSTA. Based on the capability filter information (CapabilityFilterInfo)element, the AP may determine whether to transmit a probe response frameto the STA.

Referring to FIG. 11(a), capability filter information(CapabilityFilterInfo) element 1110 may include Element ID indicating anelement identification value, Length indicating a length of thecapability filter information element, Filtering Preference indicatingpreference information regarding a response target AP, Securitycapability element indicating security capability of the STA, othercapability requested for the AP by the STA, and Othercapability/preference elements indicating further preference.

Referring to FIG. 11(b), capability filter information(CapabilityFilterInfo) element 1120 may include only an Element IDfield, a Length field, and Filtering Preference field indicatingpreference information regarding a response target AP, by deleting theforegoing Security capability element field and Othercapability/preference elements field. In this case, an effect ofshortening the length of the capability filter information element 1120is obtained.

FIG. 12 illustrates an example of a filtering preference field formatincluded in the capability filter information (CapabilityFilterInfo)element. The format of the filtering preference field according to anembodiment of the present invention is merely an example, and the fieldorder, length, or the like, may be modified as necessary. Also, some ofthe subfields included in the filtering preference field may beselectively used as necessary, and other subfield than the subfieldsdescribed hereinafter may be additionally used.

Referring to FIG. 12(a), a Filtering Preference field 1210 is a fieldindicating preference information regarding a response target AP. Here,a Filter Request subfield is a field allowing an AP to determine whetherto transmit a probe response frame to an STA in consideration of an APpolicy, or the like, based on preference and capability informationincluded in a Filter Request subfield. Namely, the AP may determinewhether to use probe request filtering which decides whether to transmita probe response frame or not based on the Filter Request subfield.

When a value of the Filter Request subfield is 1, an AP (or STA), whichhas received a probe request frame, checks capability and preference ofthe STA based on an capability filter information element andinformation such as HT capability, VHT capability, or the like, includedin the probe request frame. When the capability and preference of theSTA correspond to a policy of the AP and a supported rate indicated in asupported rate element included in the probe request frame satisfies arate supported by the AP, the AP transmits a probe response frame.Meanwhile, when a value of the Filter Request subfield is 0, the AP (orSTA), which has received a probe request frame, transmits a proberesponse frame regardless of the preference and capability informationincluded in the Filter Request subfield.

FIG. 12(b) illustrates another example of the Filtering Preference fieldformat, in which the Filter Request subfield is deleted from theFiltering Preference field 1210 illustrated in FIG. 12(a).

When the AP (or STA) receives a probe request frame including theFiltering Preference field 1220 illustrated in FIG. 12(b), the AP checkscapability and preference of the STA based on the capability filterinformation element and the information such as HT capability, VHTcapability, or the like, included in the probe request frame. When thecapability and preference of the STA correspond to a policy of the APand a supported rate indicated in a supported rate element included inthe probe request frame satisfies a rate supported by the AP, the APtransmits a probe response frame. When the AP (or STA) receives a proberequest frame not including the capability filter information element,the AP (or STA) transmits a probe response frame regardless ofpreference and capability information.

Also, when the STA wants to use security processing, a value of theRequire Security subfield of the Filtering Preference fields 1210 and1220 may be set to 1 and it may be included in the probe request frame.When a value of the Require Security subfield value is 1, a securitycapability element should be necessarily included in the capabilityfilter information element.

The security capability element indicates a security processingcapability of the STA. When a value of the security capability elementis 1, a Require No Security subfield should be necessarily set to 0.

No matter whether or not the STA supports security processingcapability, when the STA does not want security processing, the value ofthe Require No Security field is set to 1. When the value of the RequireNo Security is set to 1, the security capability element may not beincluded.

When the STA does not have particular security preference (security usedor security unused), both the Require Security subfield and the RequireNo Security subfield are set to 1. In this case, the security capabilityelement should be included in the capability filter information element.

The Require Security subfield and the Require No Security subfield mayindicate preference according to a subfield value as shown in Table 4below. The values of the subfield illustrated in Table 4 is merely anexample and may be changed, and the preference is also merely anexample.

TABLE 4 Require Require No Security Security Meaning 1 1 Requesting STAdoes not have any particular security preference Security capabilityelement should be included in CapabilityFilterInfo element 1 0Requesting STA requests to process security Security capability elementshould be necessarily included in CapabilityFilterInfo element 0 1Requesting STA requests not to process security There is no need forSecurity capability element to be included in CapabilityFilterInfoelement 0 0 Reserved

Meaning of the Require HT, Require VHT, Require non-HT included in thefiltering preference field 1210 illustrated in FIG. 12(a) and thefiltering preference field 1220 illustrated in FIG. 12(b) may beorganized as shown in Table 5 below. The values of the subfieldsillustrated in Table 5 are merely examples and may be changed, andpreference is also merely an example.

TABLE 5 Require Require Require HT VHT non-HT Meaning 1 1 1 Nopreference 1 0 0 Requesting STA wants to be associated only with HT STA0 1 0 Requesting STA wants to be associated only with VHT STA 0 0 1Requesting STA wants to be associated only with non-HT STA 1 1 0Requesting STA wants to be associated with HT STA or VHT STA 1 0 1Requesting STA wants to be associated with HT STA or non-HT STA 0 1 1Requesting STA wants to be associated with VHT STA or non-HT STA 0 0 0Reserved

Preference may be added by using the “Reserved” field illustrated inTable 4 and Table 5. For example, when the STA wants to be connected toan AP only when signal strength greater than a particular value, suchinformation may be added to the “Reserved” field and used.

FIG. 13 illustrates an example of a security capability element fieldformat included in a capability filter information(CapabilityFilterInfo) element according to an embodiment of the presentinvention.

Referring to FIG. 13, a security capability element 1310 indicatessecurity capability of an STA.

Version, Pairwise Cipher Suite Count, Pairwise Cipher Suit List, AKMSuite Count, AKM Suite List, RSN Capabilities fields in the securitycapability element 1310 may be used in the same manner as that of theRSN element of the existing 802.11. In the existing RSN element, onlyone of Group Data Cipher Suite, Group Management Cipher Suite isdesignated, but in an embodiment of the present invention, a number ofthem may be designated to allow the STA to designate several preferredCipher Suites.

A Group Data Cipher Suite Count field indicates a number of Group datacipher suite selectors indicated in a Group Data Cipher Suite List. AGroup Data Cipher Suite List includes a list of supported Group DataCipher Suites. The Group data cipher suite field is used to protect agroup addressed frame in a BSS. The Group Management Cipher Suite Countfield indicates a number of Group Management cipher suite selectorsincluded in a Group Management Cipher Suite List field. The GroupManagement Cipher Suite List field includes a list of supported GroupManagement Cipher Suites. The Group management cipher suite field isused to protect a group addressed robust management frame.

If the STA does not want to use a particular Cipher Suite although itsupports it, the corresponding Cipher Suite may not be included in thesecurity capability element 1310 and may be used for the purpose ofindicating security preference of the STA.

In case that the capability filter information element is included inthe probe request frame, when an AP (or STA), which has received theprobe request frame, determines that it can satisfy the preference ofthe STA included in the capability filter information element or whenthe STA has capability of being associated with the AP, the AP transmitsa response frame. Hereinafter, a specific example of using a proberesponse filtering method for determining whether to transmit a responseframe by an AP upon receiving a probe request frame including suchcapability filter information will be described.

When the capability filter information element is included in a proberequest frame, the AP (or STA), which has received it, transmits aresponse frame when it can satisfy preference of the requesting STAincluded in the capability filter information element or when therequesting STA has capability of being associated with the AP (or STA).

The AP (or STA) responds by a probe response frame only when thefollowing conditions are met, and when the following conditions are notmet, the AP (or STA) may not transmit a probe response frame or transmita null probe response frame.

(a) In case that the Filter Request subfield in the capability filterinformation element is set to 0, the AP (or STA) transmits a proberesponse frame as a response. Or, when both (b) and (c) as describedhereinafter are met, the AP (or STA) transmits a probe response frame.

(b) In case that the Filter Request subfield in the capability filterinformation element is set to 1,

-   -   1) the STA satisfies security processing preference stated in        the Require Security subfield and the Require No security in the        capability filter information element,    -   2) the STA satisfies preference stated in the Require HT        subfield, the Require VHT subfield, and the Require non-HT        subfield in the capability filter information element, and    -   3) the Require Security subfield is 1 and the Require No        Security subfield is 0, and when security capability of the        requesting STA satisfies the security policy of the AP, the AP        transmits a probe response frame. If both the Require Security        subfield and Require No Security subfield are set to 1 and the        STA wants security processing, the AP transmits a probe response        frame as a response only when the security capability of the        requesting STA satisfies the security policy of the AP. In case        that both the Require Security subfield and Require No Security        subfield are set to 1 and the AP does not want security        processing with respect to the requesting STA, the AP transmits        a probe response frame as a response regardless of security        capability of the requesting STA.

(c) When the Filter Request subfield of the capability filterinformation element is set to 1 and rates stated in Supported rateselement of the probe request frame transmitted by the STA support allthe rates (rates included in BSSBasicRateSet parameter) requested by theAP, the AP transmits a probe response frame as a response.

The case that security capability of the requesting STA does not satisfythe security policy of the responding AP (or STA) refers to thefollowing case.

(1) Group Data Cipher Suite, Pairwise Cipher Suite, AKM Suite, or GroupManagement Cipher Suite requested by the AP are not included in thesecurity capability element,

(2) While the AP supports CCMP or HT, the requesting STA supports onlyTKIP or a previous legacy cipher suite although the requesting STA is anHT STA,

(3) When the AP is RSNA-enabled and intends to certainly use RSNA withthe requesting STA, the AP checks a value of MFPC and MFPR of the RSNcapability field to find that these values are inappropriate for therequesting STA to be associated with the AP,

(4) when the AP is an IBSS STA and an requesting STA and an respondingIBSS STA do not support a common pairwise cipher suite subset, a commonsingle group cipher suite or a common AKMP,

(5) when the AP is an IBSS STA and the IBSS STA supports CCMP or HT,while the requesting STA is an HT STA but supports only TKIP or aprevious legacy cipher suite,

(6) when the AP is an IBSS STA, a corresponding IBSS STA isRSNA-enabled, and when RSNA is necessarily intended to be used with therequesting STA, values of MFPC and MFPR of RSN capability field of therequesting STA are checked, but the values are inappropriate for therequesting STA to be associated with the responding IBSS STA,

(7) When the AP is a Mesh STA and a requesting Mesh STA and a respondingMesh STA do not support a common pairwise cipher suite subset or acommon single group cipher suite, or

(8) When the AP is a Mesh STA and the STA supports WEP-40, WEP-104, orTKIP by pairwise cipher suite or group cipher suite.

Meanwhile, in an embodiment of the present invention, the capabilityelement illustrated in FIG. 13 may not be used and an existing RSNinformation element may be used. An existing RSN information element,instead of the security capability element, may be used in thecapability filler information element. Here, among the existing RSNinformation elements, PKMID-Count, PKMID List, or the like, are notessential, so they may not be included.

The RSN information element may include only one Group Data Cipher Suiteand one Group Management Cipher Suite, but in the security capabilityelement according to an embodiment of the present invention, the RSNinformation element extends to include a list to support several GroupData Cipher Suite and several Group Management Cipher Suite. However,for the convenience of implementation, an RSN information element may beused, and FIG. 14 illustrates an example of the capability filterinformation element using the same.

FIG. 14 illustrates another example of capability filter information(CapabilityFilterInfo) using an RSN information element according to anembodiment of the present invention.

Referring to FIG. 14, the capability filter information element 14510may include Element ID indicating an element identification value,Length indicating a length of a capability filter information element,Filtering Preference indicating preference information regarding aresponse target AP, and RSN IE indicating security capabilityinformation of an STA.

FIG. 15 illustrates another example of a security capability elementfield format included in a capability filter information(CapabilityFilterInfo) element according to an embodiment of the presentinvention.

Referring to FIG. 15(a), a security capability element 1510 may be usedby changing the security capability element 1310 illustrated in FIG. 13.Namely, the security capability element 1510 may use only one GroupManagement Cipher Suite subfield, instead of Group Management CipherSuite Count subfield and Group Management Cipher Suite List subfield ofthe security capability element 1310 illustrated in FIG. 13. The otherremaining subfields of the security capability element 1510 are the sameas those of the security capability element 1310 illustrated in FIG. 13.

As described above, the existing RSN information element may includeonly one Group Data Cipher Suite and one Group Management Cipher Suite,and the security capability element 1310 illustrated in FIG. 13 extendsto include a list supporting several subfields, and the securitycapability element 1510 illustrated in FIG. 15(a) extends such thatseveral Group Data Cipher Suite subfields, among Group Data Cipher Suiteand Group Management Cipher Suite, are included.

Referring to FIG. 15(b), a security capability element 1520 may be usedby changing the security capability element 1310 illustrated in FIG. 13.Namely, the security capability element 1520 may use only one Group DataCipher Suite subfield, instead of Group Data Cipher Suite Count subfieldand Group Data Cipher Suite List subfield of the security capabilityelement 1310 illustrated in FIG. 13. The other remaining subfields ofthe security capability element 1520 are the same as those of thesecurity capability element 1310 illustrated in FIG. 13.

As described above, the existing RSN information element may includeonly one Group Data Cipher Suite and one Group Management Cipher Suite,and the security capability element 1310 illustrated in FIG. 13 extendsto include a list supporting several subfields, and the securitycapability element 1510 illustrated in FIG. 15(b) extends such thatseveral Group Management Cipher Suite subfields, among Group Data CipherSuite and Group Management Cipher Suite, are included.

FIG. 16 illustrates another example of a security capability elementfield format included in a capability filter information(CapabilityFilterInfo) element according to an embodiment of the presentinvention.

Referring to FIG. 16, a security capability element 1610 may be used bychanging the security capability element 1310 illustrated in FIG. 13,and includes an Element ID field, a Length field, and an RSNCapabilities field.

Recently manufactured wireless LAN products support most of theciphering algorithms required in an RSN standard in many cases, so anincrease in the size of the probe request frame may be minimized byincluding only the RSN Capabilities field while deleting cipheringalgorithm information in the security capability element 1310illustrated in FIG. 13.

Here, the RSN Capabilities field may be configured in the form of asubfield in the capability filter information (CapabilityFilterInfo)element of FIG. 17 as described hereinafter, rather than generating theelement form as illustrated in FIG. 16.

FIG. 17 illustrates another example of the capability filter information(CapabilityFilterInfo) element according to an embodiment of the presentinvention.

Referring to FIG. 17, a capability filter information(CapabilityFilterInfo) element 1710 may include Element ID indicating anelement identification value, Length indicating a length of a capabilityfilter information element, Filtering Preference indicating preferenceinformation regarding a response target AP, RSN Capabilities indicatingRSN capability of a requesting STA, other capability requested for an APby a requesting STA, Other capability/preference elements furtherindicating preference. In this case, the length of the capability filterinformation element 1710 is shortened.

As described above, the capability information regarding a station andpreference information regarding a response target AP according to anembodiment of the present invention may be included in a probe requestframe by using the RSN information element. Here, only the RSNcapability field, among the fields in the existing RSN element, may beincluded in the probe request frame. The RSN capabilities elementincluding the RSN capabilities field may have such a form as illustratedin FIG. 16. Namely, the recently manufactured wireless LAN productssupport most of the ciphering algorithms required in an RSN standard inmany cases, so an increase in a size of a probe request frame may beminimized by including only the RSN Capabilities field while deletingciphering algorithm information from the existing RSN element.

Meanwhile, as described above, although capability information regardinga requesting station satisfies the policy of the responding AP (or STA)and preference information regarding a response target AP is satisfiedby the responding AP (or STA), if a current load of the responding AP(or STA) is heavy or the AP (or STA) cannot additionally receive anassociation request from the STA, the AP (or STA) may not transmit aprobe response frame to the STA or may transmit a null probe responseframe to prevent the STA from being associated.

FIG. 18 illustrates another example of capability filter information(CapabilityFilterInfo) according to an embodiment of the presentinvention.

The capability filter information (CapabilityFilterInfo) may includeadditional information to allow the AP to perform filtering elaborately.By using the capability filter information element including suchadditional information, the AP may elaborately determine whether totransmit a probe response frame.

Referring to FIG. 18(a), a capability filter information(CapabilityFilterInfo) 1810 may additionally include a SupportedCredential Type indicating credential type information supported by anSTA.

For example, the Supported Credential Type field may indicate credentialinformation as to whether an STA supports a SIM, a USIM, or an NFC,whether the STA uses a Pre-Shared key, whether the STA supports X 509authentication certificate, whether the STA supports a Username/Passwordscheme, whether the STA uses One Time Password, whether the STA supportsonly server-side authentication, or the like. The Supported CredentialType field including such credential information may be configured asillustrated in FIG. 18(b).

The order and length of the Supported Credential Type field illustratedin FIG. 18(a) may be modified, and the Supported Credential Typeillustrated in FIG. 18(b) may include only a particular field asnecessary.

The requesting STA includes information regarding a security tokensupported by the STA, a credential type, a supportable authenticationmethod, and the like, in a probe request frame and transmits the frame,and when the requesting STA does not support the credential required forauthentication by the AP, the AP does not transmit a probe responseframe because the STA cannot be associated to the AP.

However, in the related art, in order for the STA to know a credentialtype required for an authentication scheme supported by a particular AP,the STA transmits a probe request frame, receives a probe responseframe, and checks whether the corresponding AP supports an advertisementfunction (ANQP) of 802.11u. Upon checking, the STA receives securitycredential information from the corresponding AP through a GAS query,checks whether the corresponding credential is supported, and attemptsassociation, causing inconvenience. Thus, when the credentialinformation supported by the STA is included in a probe request frame,such an additional query/response process is not required to beperformed, and when the STA does not support credential information,filtering may be immediately performed to make the association processfast.

FIG. 19 illustrates another example of capability filter information(CapabilityFilterInfo) according to an embodiment of the presentinvention.

Referring to FIG. 19, the capability filter information(CapabilityFilterInfo) element 1910 may additionally include a SupportedChannels field indicating channel information supported by an STA. Byadding the Supported Channels field, the AP may perform filtering moreelaborately.

The Supported Channels field is a list of channel subbands supported bythe STA, in which a pair of a first channel number and a number ofchannel of a channel subband supported by the STA may be repeatedlyincluded. Of course, a supported channel information may be expressed ina different manner.

For example, upon recognizing supported channels information of the STA,if the AP does not support a channel requested by the STA, the AP doesnot transmit a probe response frame.

FIG. 20 illustrates another example of a Filtering Preference fieldformat included in a capability filter information(CapabilityFilterInfo) element according to an embodiment of the presentinvention. The Filtering Preference field may include Internet accesspreference information as preference information regarding a responsetarget AP.

Referring to FIG. 20, a Filtering Preference field 2010 may include aRequire Internet Access subfield indicating whether an STA wantsInternet access. The other remaining subfields excluding the RequireInternet Access subfield, may be configured to be the same as those ofthe filtering preference field 1220 illustrated in FIG. 12(b).

For example, when the STA wants Internet access, the STA may set a valueof the Require Internet Access subfield as 1, includes it in a proberequest frame, and transmits the same. Upon receiving it, when an APdoes not support the Internet access of the STA, the AP does nottransmit a probe response frame. Meanwhile, when a value of the RequireInternet Access subfield is set to 0, since the STA does not wantInternet access, the AP may transmit a probe response frame.

Meanwhile, in case that a load of the AP is heavy, when a channel stateis poor, or when admission capacity is full, although the AP transmits aprobe response frame to the STA, there is a high possibility of failurewhen the STA requests association to the AP afterwards. In this case,when the AP is not available for an association of a new STA inconsideration of its operating situation, the AP may not transmit aprobe response frame. Also, the STA may explicitly request an operationcondition from the AP.

FIG. 21 illustrates an example of information included in an APoperating condition preference element according to an embodiment of thepresent invention. The AP operating condition preference element may notbe a form of an information element and the STA may include desired APoperating condition preference information in a probe request frame byusing an appropriate format and transmit the same to the AP. Also, theAP operating condition preference element may be included in theforegoing capability filter information element, or may be configured asa separate element or field and included in a probe request frame.

Referring to FIG. 21(a), an AP operating condition preference element2110 may include Element ID indicating an element identification value,Length indicating a length of the AP operating condition preferenceelement, AP Access Delay requirement indicating requirements withrespect to AP access delay such as current average access delay of anAP, access delay of each access category, and the like, AP AvailableAdmission Capacity Requirement indicating requirements with respect tocurrent admission capacity of the AP, and Other AP operating conditionrequirement for requesting operating condition with respect to otherAPs.

For example, in case that a maximum value of current average accessdelay of the AP, access delay of each access category, and the like is100, when the STA sets the numeral value as 90 or smaller in an APAccess Delay requirement and transmits a probe request frame, if a delaynumerical value of the AP exceeds 90, the AP does not transmit a proberesponse frame because it does not satisfy the delay level required bythe STA. Also, in case that the STA requests extra admission capacity as10 in an AP Available Admission Capacity Requirement field, when acurrent situation of the AP has admission capacity less than 10, the APdoes not transmit a probe response frame.

Also, as illustrated in FIG. 21(b), an AP operating condition preferenceelement 2110 may further include requirements of the STA with respect toa current situation such as a current spatial stream utilization of theAP, channel utilization of each band, and the like.

When the AP, which has received a probe request frame including theforegoing AP operating condition preference element, has a heavy load soit cannot satisfy the access delay, admission capacity, and leeway ofchannel utilization, the AP does not transmit a probe response frame tothe STA to prevent the STA from unnecessarily attempting an association.

Meanwhile, the STA may include network preference information regardinga service type of a network connected through the AP, a supportedprotocol, an access scheme supported by the network, a venue in whichthe network is located, and the like, in a probe request frame andtransmit the same. Upon receiving the probe request frame including suchinformation, if the AP does not satisfy the network preferenceinformation of the STA, the AP does not transmit a probe response frame.Hereinafter, AP network preference information preferred by the STA willbe described with reference to FIG. 22.

FIG. 22 illustrates an example of information included in an AP networkpreference element according to an embodiment of the present invention.The AP network preference element may not necessarily be a form of aninformation element and the STA may include its desired AP networkpreference information in a probe request frame by using an appropriateformat and transmit the same to the AP. Also, the AP network preferenceelement may be included in the foregoing capability filter informationelement or may be configured as a separate element or field and includedin the probe request frame.

Referring to FIG. 22(a), the AP network preference element 2210 mayinclude Network Filtering Control, Preferred Advertisement Protocolindicating a preferred network protocol, Supported Device typeindicating a device type supported by an STA, Preferred Access Networkindicating information regarding a preferred access network, RequiredService indicating information regarding a service desired to be usedthrough an AP, and Reserved reserved for different informationafterwards.

The Network Filtering Control field will be described in detail withreference to FIG. 22(b).

The Preferred Advertisement Protocol field may include network discoveryprotocol demand, such as ANQP supported in 802.11u, support demand ofEmergency Alert system protocol, MIH Information Service, MIH Commandand Event Service Capability Discovery, or the like, the STA wants touse to discover an AP. For example, when the STA wants to use thenetwork discovery function but the AP does not support it, the AP doesnot transmit a probe response frame. The Preferred AdvertisementProtocol field including such information may be configured as shown inFIG. 22(c).

The Supported Device type field may indicate whether the STA is a smartphone, a VoIP phone, a notebook computer, a game console, a digitalcamera, a printer, or the like. When such information is included in theprobe request frame and transferred to the AP, if the AP permits only anaccess of a particular device or does not support a service with respectto the corresponding device, the AP does not transmit a probe responseframe.

The Preferred Access Network field may indicate a type of an accessnetwork the STA wants to use. For example, WLAN, 3GPP, WiMAX, or thelike, may be stated in the Preferred Access Network field andtransmitted to the AP. In case that the STA uses WLAN and does not wantto be automatically switched to 3GPP due to a problem such as a chargeincurrence, or the like, by an ISP, the STA may set WLAN require=1, 3GPPrequire=0″, or the like, in the Preferred Access Network, to thus statepreference with respect to an forcible access of the user's STA to adifferent network by a network provider. The Preferred Access Networkfield may be configured as shown in FIG. 22(d).

The Required Service field may indicate information regarding a service,e.g., a printing service, a VoIP service, a streaming service, Websurfing, or the like, the STA wants to use through an AP.

Also, in the existing 802.11, “venue type” information is included in aprobe response frame, or the like, and when an STA does not want toaccess a particular venue, corresponding information is provided to theAP, and when the AP does not support it, the AP does not transmit aprobe response frame. Here, since the element indicating venueinformation exists in the existing 802.11, it may be utilized to definea venue or a “venue type” may be newly defined to be optimized for aprobe request frame.

For example, the STA includes a venue, of which a network the STA is toaccess, in the “venue info” of an interworking element of the proberequest frame to allow an AP, which has received the probe requestframe, to determine whether to transmit a probe response frame. Uponchecking the venue type, if the AP cannot access the venue, the AP maynot transmit a probe response frame.

Also, the AP network reference element 2210 may further include RCPI,RSNI requirements, and the like, of the AP, to allow the AP not totransmit a probe response frame if the AP does not support correspondinglink quality.

Referring to FIG. 22(b), a Network Filtering Control field may includeFilter by supported Adv Protocol indicating performing of filteringallowing not to transmit a probe response frame if a protocol requestedby an STA is not included in advertisement protocols (e.g., ANQP, MIHInformation Service, MIH Command and Event Services CapabilityDiscovery, Emergency Alert System, or the like) supported by an AP,Filter unsupported device type indicating performing filtering if an APdoes not support a device type stated by an STA or the AP does notpermit an access thereto, Filter by Access Network Preference indicatingperforming filtering if requirements with respect to an access network,such as WLAN, 3GPP, WiMAX, or the like, desired by an STA are not met,Filter by supported venue indicating performing filtering ifrequirements with respect to a venue desired to be accessed by an STAare not met, and Filter by supported service indicating performingfiltering if a service desired to be used by an STA is not supported.

Meanwhile, as described above, a probe request frame according to anembodiment of the present invention may include information indicating aduration in which a probe response frame with respect to the proberequest frame can be received by the transmitting STA of the proberequest. For example, the probe request frame may include a TimeoutInterval element indicating a duration in which a station that hastransmitted the probe request waits to receive a probe response frame onone channel. Also, in another embodiment, the probe request frame mayinclude a Probe Response listen start interval element indicating atiming at which a probe response frame starts to be received after theprobe request frame is transmitted with respect to one channel.

An example of a format indicating a Timeout interval element isillustrated. The timeout interval may be used in any form as long as itmay be included in a probe request frame.

The Timeout Interval element and the Probe Response listen startinterval element may be used by extending the Timeout Interval element(TIE) present in the existing 802.11 standard. Namely, it may be used byassigning one of reserved values of the Timeout Interval element (TIE)of the existing 802.11 standard.

In Table 6 shown below, the Timeout Interval element is assigned byusing No. 5 of the Timeout Internal Type, but it is merely illustrativeand a different value of the Timeout Interval Type may be assigned.

Also, in case of using the Probe Response listen start interval element,No. 6 of the Timeout Interval Type may be assigned, but it is merelyillustrative and any other values may be assigned.

TABLE 6 Timeout Interval Type Meaning Units 0 Reserved 1 Reassociationdeadline interval Time units (TUs) 2 Key lifetime interval Seconds 3Association Comeback time Time units (TUs) 4 Time-to-Start Time units(TUs) 5 ProbeResponse deadline interval Time units (TUs) 6 ProobeResponse listen start interval Time units (TUs) 7-255 Reserved

When the Timeout Interval element (TIE) of the existing 802.11 standardis extended to be used, an existing element is advantageously utilizedwithout having to define a new element. If a probe response listen startinterval is stated in the Timeout Interval element (TIE) of the existing802.11 standard, a TIE indicating a timeout interval element and a TIEindicating a probe response listen start interval element, namely, twoTIEs, are added to a probe request frame. Meanwhile, when the proberesponse listen start interval is not used, only the TIE indicating atimeout interval element may be included in the probe request frame.

Response reception time information regarding a probe request frame,i.e., timeout interval information or timeout interval information withprobe response listen start interval information may be included in aprobe request frame by defining a new element.

FIG. 23 is a view illustrating an example of a Timeout Interval elementand a Probe Response listen start interval element according to anembodiment of the present invention.

Referring to FIG. 23(a), a Timeout Interval element 2310 may includeElement ID indicating an identification value of an element, Lengthindicating a length of the Timeout Interval element, and TimeoutInterval Value indicating a duration in which a STA that has transmittedthe probe request waits for corresponding probe responses frame on onechannel.

Here, in the Timeout Interval Value field, the timeout interval may beindicated by a time unit (TU) or a different unit such as microsecond,or the like. Also, as for a length of the Timeout Interval Value field,one octet, two octets, or any longer length may be allocated accordingto a used time unit or an allowable maximum time. In the presentembodiment, for the description purpose, two octets are illustrated, butin case of an actual application, the length of the Timeout IntervalValue field may be shorter or longer as necessary.

Referring to FIG. 23(b), a Probe Response listen start interval element2320 may include Element ID indicating an identification value of anelement, Length indicating a length of a probe response listen startinterval element, and Probe Response listen start Interval Valueindicating a time in which a STA starts to receive a probe responseframe after transmitting a probe request frame on one channel.

Here, in the Probe Response listen start Interval Value field, the proberesponse listen start interval may be indicated by a time unit (TU) or adifferent unit such as microsecond, or the like. Also, as for a lengthof the Probe Response listen start Interval Value field, one octet, twooctets, or any longer length may be allocated according to a used timeunit or an allowable maximum time. In the present embodiment, for thedescription purpose, two octets are illustrated, but in case of anactual application, the length of the Probe Response listen startInterval Value field may be shorter or longer as necessary.

In case of defining and using a new element as described above, if aprobe response listen start interval element is used for indicating theresponse reception time information, a timeout interval element and aprobe response listen start interval element are added to a proberequest frame. Meanwhile, if the probe response listen start intervalelement is not used, only the timeout interval element may be includedin the probe request frame.

Also, as illustrated in FIG. 23(c), the timeout interval element and theprobe response listen start interval element may be defined in the formof one element and used. Here, the Length field may have a variablelength. As described above, the Timeout Interval Value field and theProbe Response listen start Interval Value may be indicated by a timeunit (TU) or a different unit such as microsecond, or the like. Also, asfor a length of the Timeout Interval Value field and the Probe Responselisten start Interval Value field, one octet, two octets, or any longerlength may be allocated according to a used time unit or an allowablemaximum time. In the present embodiment, for the description purpose,two octets are illustrated, but in case of an actual application, thelength of the Probe Response listen start Interval Value field may beshorter or longer as necessary.

If the probe response listen start interval element is not used, theProbe Response listen start Interval Value is omitted, and here, theLength field may be set to 2. Also, order of the Timeout Interval Valuefield and the Probe Response listen start Interval Value field may bechanged and may be included in a probe request frame and transmitted.

As described above, the use of the timeout interval element or the proberesponse listen start interval element as an information element form ismerely an example, and it may be configured as a general subfield formand included in the probe request frame. Or, it may be included in theform of a subfield in a third information element or field and thecorresponding information element or field may be included in the proberequest frame.

The probe request frame according to an embodiment of the presentinvention may include at least one of the inclusion list, the exclusionlist, capability information regarding a station, preference informationregarding a response target AP, and response reception time informationwith respect to a probe request frame, and a method as shown in Table 7below may be used. Table 7 shows an example of information that may beincluded in a probe request frame, and the present invention is notlimited thereto.

TABLE 7 Order Information Notes x RSN, capability Method 1: Existing RSNelement is included. filter information (RSN element is included whendot11RSNAActivated is (CapabilityFilterInfo), true and RSN element isselectively included when or RSN dot11FILSActivated is true)capabilities Method 2: Newly defined capability filter information(CapabilityFilterInfo) is used. (CapabilityFilterInfo element isselectively included when dot11FILSActivated is true) Method 3: RSNcapabilities element including only RSN capabilities in the fields ofthe existing RSN element is included. (RSN capabilities element isselectively included when dot11FILSActivated is true) These methods areexamples, and preference information (whether AP is HT/VHT, preferenceof STA with respect to AP, load of AP, requirements with respect toadmission capacity, resource utilization requirements of AP, Internetaccess request, credential supported by STA, security token information,supported channel, preferred network, etc.) of STA with respect to APmay be included. x Timeout Interval Method 1: Timeout Interval elementof existing standard is (or utilized. Only type is added to be used.ProbeResponse (Timeout Interval element (TIE) including timeout Intervaldeadline interval) is included when dot11FILSActivate is true and any ofthe fields in the element are nonzero) Method 2: Timeout Intervalelement is newly defined to be used. x Probe Response Method 1: TimeoutInterval element of existing standard is Listen Start utilized. Onlytype is added to be used. Interval (Probe Response Listen Start Interval(TIE) including ProbeResponse deadline interval is included whendot11FILSActivated is true and any of the fields in the element arenonzero) Method 2: Probe Response Listen Start Interval is newly definedto be used. x Inclusion List Inclusion List element is selectivelyincluded when dot11FILSActivated is trueand any of the fields in theelement are nonzero. x Exclusion List Exclusion List element isselectively included when dot11FILSActivated is true and any of thefields inthe element are nonzero.

Meanwhile, the null probe response frame according to an embodiment ofthe present invention is a frame in which a frame body is removed froman existing probe response frame. Upon receiving the null probe responseframe, the STA does not attempt association (or peering) to thecorresponding AP (or STA), and adds the corresponding AP (or STA) in theexclusion list, so that it may not transmit a probe request frame to thecorresponding AP (or STA). Also, when the corresponding AP (or STA) isincluded in the inclusion list, the STA may delete it.

In an embodiment, a Reason code field may be included in a frame body ofa null probe response frame. In this case, it is used in the same manneras the case in which the frame body is all eliminated, but when aspecific reason for not being able to be associated is included in thereason code field and transmitted, the STA may receive detailedinformation.

The AP (or STA) may not transmit a null probe response frame and may nottransmit a probe response frame. In this case, an effect of reducing aprobe response frame is increased, and the STA may still be preventedfrom being erroneously associated to an AP.

FIG. 24 is a flow chart illustrating a process of performing activescanning by an STA that transmits a probe request frame according to anembodiment of the present invention. The process in which the STAillustrated in FIG. 24 performs active scanning is a processingprocedure combining active scanning methods according to an embodimentof the present invention as described above, and is an example of one ofpossible combinations of the active scanning methods according to anembodiment of the present invention as described above.

Referring to FIG. 24, the STA generates a probe request frame (S2400).Here, the STA may include information regarding a response target AP inthe probe request frame.

For example, the STA may include BSSID, SSID, SSID List, HESSID, MeshID,or the like, in the probe request frame to range a range of a responsetarget AP (or mesh STA or STA of IBSS). Also, the STA may include theforegoing inclusion list or exclusion list in the probe request frame.Also, the STA may include the RSN information element or capabilityfilter information element in the probe request frame to inform an APabout the capability information of the STA, and preference informationregarding a response target AP. Also, the STA may include a timeoutinterval as reception time information for waiting a probe responseframe in the probe request frame. Details of a method for configuringthe information to be included in the probe request frame have beendescribed above so a description thereof will be omitted.

The STA transmits the probe request frame via a selected channel in abroadcast or unicast manner (S2410).

The STA may receive a probe response frame from at least one responsetarget AP based on the information regarding a response target APincluded in the probe request frame, and when the probe response frameis successfully received, the STA transmits an ACK frame to the AP (ormesh STA or STA of IBSS) (S2420). If the selected channel is inactiveduring a minimum channel time, the STA returns to step S2460 and selectsa next channel to be scanned.

The STA checks whether a maximum channel time has lapsed (S2430). Whenthe maximum channel time has not lapsed, the STA repeatedly performs ofreturning to step S2420, receiving a probe response frame, andtransmitting an ACK frame. Meanwhile, when the maximum channel time haslapsed, the STA stops scanning a corresponding selected channel.

According to an intermediate scanning result, when a generation optionfor intermediate result has been set, the STA generates intermediateresults scanned up to a current timing (S2440).

The STA checks whether a scan abort has been requested (S2450).

When a scan abort request has been received, the STA generates a finalreport with respect to a scanned AP up to a termination timing. The scanabort request may be received at any timing during a scanning process,and when the scan abort request is received, scan results up to thetiming at which the scan abort request is received are generated as afinal report and returned.

When a scan abort request has not been received, the STA checksinformation regarding an AP channel from the received probe responseframe, and when information regarding an AP channel is included in theprobe response frame, the STA selects a channel not scanned yet, as anext channel to be scanned based on the information (S2460). Forexample, when an AP channel is 2.4 GHz, the STA may preferentiallyselect channels 1, 6, and 11, and when a measurement pilot is received,the STA may utilize channel information, AP information, and the likeincluded therein. If there is no such information, the STA sequentiallyselects a next channel.

The STA checks whether there is a next channel to be scanned (S2470).When a next channel to be scanned exists, the STA may return to stepS2410 and transmit a probe request frame to the next channel.

Meanwhile, when a next channel to be scanned does not exist, the STAgenerates a final report with respect to an AP scanned up to a currenttiming (S2480), terminates the scanning process, and returns a finalreport (S2490).

FIG. 25 is a flow chart illustrating a process of performing activescanning by an AP which receives a probe request frame according to anembodiment of the present invention. The process of performing activescanning by the AP illustrated in FIG. 25 is a procedure combining theactive scanning methods according to an embodiment of the presentinvention as described above, and illustrates one of availablecombinations of the active scanning method according to an embodiment ofthe present invention as described above.

Referring to FIG. 25, an AP (or a mesh STA, or an STA of an IBSS)receives a probe request frame (S2500).

The AP (or the mesh STA or STA of IBSS) checks information regarding aresponse target AP included in the received probe request frame (S2510).For example, the AP may check SSID, BSSID, SSID List, HESSID, MeshID,inclusion list, exclusion list, and the like, included in the proberequest frame.

The AP (or the mesh STA or STA of IBSS) determines whether the AP is aresponse target AP (S2520). When the AP (or the mesh STA or STA of IBSS)is not a response target AP, the AP terminates the responding processwith respect to the received probe request frame.

Meanwhile, when the AP (or the mesh STA or STA of IBSS) is a responsetarget AP, the AP checks capability information regarding an STA andpreference information regarding an AP included in the received proberequest frame (S2530). For example, the AP may check an RSN informationelement, capability filter information element, and the like, of theprobe request frame. Also, the AP (or the mesh STA or STA of IBSS) maycheck its current load state, or the like. The capability informationregarding an STA and the preference information regarding an AP includedin the probe request frame has been described in detail above, so adescription thereof will be omitted.

The AP (or the mesh STA or STA of IBSS) determines whether it satisfiespreference of the STA based on the capability information regarding anSTA and preference information regarding an AP included in the receivedprobe request frame (S2540) that are necessary for association with theSTA. Also, the AP (or the mesh STA or STA of IBSS) may determine whetherit is capable of accommodating the STA in consideration of its currentstate.

If the AP (or the mesh STA or STA of IBSS) determines that it will notpermit an association of the STA later or the AP (or the mesh STA orIBSS STA) does not satisfy preference of the STA, the AP (or the meshSTA or STA of IBSS) may not transmit a probe response frame or maytransmit a null probe response frame without a frame body to the STA toinform the STA that an association of the STA later will not bepermitted, or may transmit a null probe response frame including areason code to even inform the STA about the reason of not permitting anassociation of the STA later (S2545). And, the AP (or the mesh STA orSTA of IBSS) terminates the responding process with respect to thereceived probe request frame.

Meanwhile, when the AP (or the mesh STA or STA of IBSS) determines thatit will permit an association of the STA later or when it satisfiespreference of the STA, the AP (or the mesh STA or STA of IBSS) checkstimeout interval information regarding a response reception timeincluded in the probe request frame, and determines whether the responsereception time has lapsed by comparing the timeout interval informationwith the duration from a timing at which the probe request frame wasreceived to a current time (S2550). When the response reception time haslapsed, the AP (or the mesh STA or STA of IBSS) does not transmit aprobe response frame and terminates the process.

Meanwhile, when the timeout interval has not lapsed, the AP (or the meshSTA or STA of IBSS) transmits a probe response frame (S2560).

The AP (or the mesh STA or STA of IBSS) checks whether an ACK frame withrespect to the probe response frame has been received (S2570).

When an ACK frame has been successfully received, it means that theprobe response frame was successfully transmitted, so the AP (or themesh STA or STA of IBSS) terminates the probe response frame processingprocedure (S2580).

Meanwhile, when the ACK frame has not been successfully received, aprobe response frame should be retransmitted. Thus, the AP (or the meshSTA or STA of IBSS) returns to the step S2550, determines whether thetimeout interval has lapsed at a current timing, and retransmits a proberesponse frame or terminates the probe response frame processingprocedure.

FIG. 26 is a block diagram of a wireless device to which an embodimentof the present invention is applicable. The wireless device may be anSTA or an AP.

Referring to FIG. 26, a wireless device 2600 includes a processor 2610,a memory 2620, and a transceiver 2630.

The processor 2610 implements a function of the STA or the AP in theforegoing embodiments. The processor 2610 generates a probe requestframe including information regarding a response target AP (inclusionlist, exclusion list), capability information regarding a station,preference information regarding a response target AP, informationregarding a response reception time with respect to a probe requestframe, and the like. Also, the processor 2610 may determine whether totransmit a probe response frame in response to the probe request frameincluding the foregoing information, and transmit a probe responseframe, transmit a null probe response frame, or may not transmit a proberesponse frame.

The memory 2620 may generate and store a probe request frame includinginformation regarding a response target AP (inclusion list, exclusionlist), capability information regarding a station, preferenceinformation regarding a response target AP, information regarding aresponse reception time with respect to a probe request frame, and thelike. Also, the memory 2620 may receive and store a probe request frameand a probe response frame according to an embodiment of the presentinvention.

The transceiver 2630 may transmit or receive a radio signal andimplements a physical layer of the IEEE 802.11 standard. For example, aphysical layer supporting HT, VHT, or the like, may be implemented.

The processor 2610 and/or the transceiver 2630 may include an ASIC(Application-Specific Integrated Circuit), a chip set, a logical circuitand/or a data processor. The memory 2620 may include a ROM (Read-OnlyMemory), a RAM (Random Access Memory), a flash memory, a memory card, astorage medium, and/or any other storage devices. When the embodimentsare implemented by software, the foregoing techniques may be implementedby modules (processes, functions, or the like) performing the foregoingfunctions. The modules may be stored in the memory 2620 and executed bythe processor 2610. The memory 2620 may be provided within or outsidethe processor 2610, or may be connected to the processor 2610 through awell-known unit.

In an embodiment of the present invention, information items added to aprobe request frame are designed to be compatible in operating withlegacy STAs (or APs). Also, in an embodiment of the present invention,information items added to a probe request frame are defined asinformation elements, and since a legacy WLAN STA (or AP) disregards it,they are operable without any problem although the legacy STA (or AP)exists in the WLAN system. When the legacy STA (or AP) receives a proberequest frame according to an embodiment of the present invention, thelegacy STA (or AP) operates according to an active scanning procedure ofthe existing 802.11.

While some exemplary embodiments of the present invention have beendescribed with reference to the accompanying drawings, those skilled inthe art may change and modify the present invention in various wayswithout departing from the essential characteristic of the presentinvention. Accordingly, the disclosed embodiments should not beconstrued to limit the technical spirit of the present invention, butshould be construed to illustrate the technical spirit of the presentinvention. The scope of the technical spirit of the present invention isnot limited by the embodiments, and the scope of the present inventionshould be interpreted based on the following appended claims.Accordingly, the present invention should be construed to cover allmodifications or variations induced from the meaning and scope of theappended claims and their equivalents.

What is claimed is:
 1. A scanning method in a wireless local areanetwork (WLAN) system, the method comprising: transmitting, by astation, a probe request frame, via a channel; and receiving, by thestation, a probe response frame from a target access point (AP) torespond to the probe request frame based on information indicated by theprobe request frame, wherein the information indicated by the proberequest frame includes at least one of information regarding a maxchannel time and preference information regarding the target AP, whereinthe information regarding the max channel time includes informationindicating a time that the station is available after transmission ofthe probe request frame to receive the probe response frame as responseswith respect to the probe request frame in the channel, wherein when themax channel time is lapsed, the probe response frame is not transmittedby the target AP, and wherein the preference information regarding thetarget AP indicates what the target AP needs to satisfy to transmit theprobe response frame to the station.
 2. The method of claim 1, whereinwhen the information regarding the response reception time is includedin the probe request frame, the station receives the probe responseframe from the target AP during the response reception time indicated inthe probe request frame, after transmitting the probe request frame. 3.The method of claim 1, wherein the preference information regarding thetarget AP includes information indicating preferences on capability ofthe target AP including information indicating preference with respectto high throughput (HT) capability of the target AP which responds tothe probe request frame and information indicating preference withrespect to very high throughput (VHT) capability of the target AP, andthe STA receives the probe response frame from the target AP in casethat the target AP satisfies the preference information regarding thetarget AP indicated in the probe request frame.
 4. The method of claim3, wherein the preference information regarding the target AP furtherincludes at least one of information indicating preference with respectto access delay of the target AP, information indicating preference withrespect to link quality of the target AP, information indicatingpreference with respect to an operating condition of the target AP,information indicating preference with respect to a network of thetarget AP, wherein in case that the preference information regarding thetarget AP is included in the probe request frame, the station receivesthe probe response frame from the target AP satisfying the preferenceinformation regarding the target AP.
 5. The method of claim 1, whereinwhen the station generates intermediate scanning results with respect tothe response target AP and discovers an AP to be associated based on thegenerated intermediate scanning results, the station instructs scanningabort in the middle of the scanning.
 6. The method of claim 1, furthercomprising: selecting, by the station, a next channel to be scannedbased on information regarding a neighbor AP included in the proberesponse frame, wherein the information regarding a neighbor AP includesa neighbor report.
 7. The method of claim 1, wherein the informationregarding a response reception time further includes informationindicating a time at which the station starts to receive the proberesponse frame, and in case that the information indicating a time atwhich the probe response frame starts to be received is included in theprobe request frame, the station receives the probe response frame fromthe target AP during the response reception time indicated in the proberequest frame starting from the time at which the probe response framestarts to be received that is indicated in the probe request frame,after transmitting the probe request frame.
 8. The method of claim 1,wherein the probe request frame further includes list informationregarding an AP which is to respond to the probe request frame by usingat least one of an SSID (Service Set Identifier), a BSSID (Basic ServiceSet Identifier), an MESHID (Mesh Identifier), an HESSID (ExtendedService Set Identifier), and a Network ID of the AP which should respondto the probe request frame.
 9. The method of claim 1, wherein the proberequest frame further includes list information regarding an AP whichshould not respond to the probe request frame by using at least one ofan SSID (Service Set Identifier), a BSSID (Basic Service SetIdentifier), an MESHID (Mesh Identifier), an HESSID (Extended ServiceSet Identifier), and a Network ID of the AP which should not respond tothe probe request frame.
 10. The method of claim 1, wherein the proberequest frame includes capability information regarding the station,wherein the capability information regarding the station includes atleast one of extended capability information, high throughput capabilityinformation, very high throughput capability information, and securitycapability information.
 11. The method of claim 1, further comprising:discovering, by the station, an AP to be associated by receiving atleast one of short beacon frames, measurement pilot frames, short proberesponse frames, probe response frames transmitted in a broadcastmanner, and probe response frames transmitted according to a requestfrom other stations.
 12. The method of claim 1, wherein the proberesponse frame is discarded based on the information regarding aresponse reception time.
 13. The method of claim 1, wherein in case themax channel time is lapsed, the target AP does not transmit the proberesponse frame to the station.
 14. The method of claim 1, wherein incase the target AP does not satisfies the preference information, thetarget AP does not transmit the probe response frame to the station. 15.A scanning method in a wireless local area network (WLAN) system, themethod comprising: receiving, by an access point (AP), a probe requestframe from a station; determining, by the AP, that the AP satisfies thepreference information regarding the target AP; and transmitting, by theAP, a probe response frame to the station, wherein the probe requestframe includes at least one of information regarding a max channel timeand preference information regarding a target AP to respond to the proberequest frame, wherein the information regarding the max channel timeincludes information indicating a time that the station is availableafter transmission of the probe request frame to receive the proberesponse frame as responses with respect to the probe request frame inthe channel, wherein when the max channel time is lapsed, the proberesponse frame is not transmitted by the AP, and wherein the preferenceinformation regarding the target AP indicates what the AP needs tosatisfy to transmit the probe response frame to the station.
 16. Themethod of claim 15, wherein the preference information regarding thetarget AP includes information indicating preferences on capability ofthe AP including information indicating preference with respect to highthroughput (HT) capability of the target AP which responds to the proberequest frame and information indicating preference with respect to veryhigh throughput (VHT) capability of the target AP, and when the APsatisfies the preference information regarding the target AP indicatedin the probe request frame, the AP transmits the probe response frame tothe station, and when the AP does not satisfy the preference informationregarding the target AP, the AP does not transmit the probe responseframe to the station.
 17. The method of claim 16, wherein the preferenceinformation regarding the target AP further includes at least one ofinformation indicating preference with respect to access delay of thetarget AP, information indicating preference with respect to linkquality of the target AP, information indicating preference with respectto an operating condition of the target AP, information indicatingpreference with respect to a network of the target AP, wherein in casethat the preference information regarding the target AP is included inthe probe request frame, when the AP satisfies the preferenceinformation regarding the target AP, the AP transmits the probe responseframe to the station, and when the AP does not satisfy the preferenceinformation regarding the target AP, the AP does not transmit the proberesponse frame to the station.
 18. The method of claim 15, wherein theprobe response frame includes information regarding a neighbor AP,wherein the information regarding a neighbor AP includes a neighborreport.
 19. The method of claim 15, wherein the information regarding aresponse reception time further includes information indicating a timeat which the station starts to receive the probe response frame, and incase that the information indicating a time at which the probe responseframe starts to be received is included in the probe request frame, theAP does not transmit the probe response frame to the station until atime at which the probe response frame starts to be received is reached,and transmits the probe response frame to the station during theresponse reception time indicated in the probe request frame startingfrom the time at which the probe response frame starts to be receivedthat is indicated in the probe request frame.
 20. The method of claim15, wherein the probe request frame includes capability informationregarding the station, and the AP determines whether to permit anassociation of the station thereto when the AP receives an associationrequest from the station based on the capability information regardingthe station, and in case that the AP decides to permit an association ofthe station thereto, the AP transmits the probe response frame, and incase that the AP decides not to permit an association of the stationthereto, the AP does not transmit the probe response frame to thestation or transmits a null probe response frame to the station.
 21. Themethod of claim 15, wherein the probe request frame includes at leastone of list information regarding an AP which should respond to theprobe request frame and list information regarding an AP which shouldnot respond to the probe request frame, and in case that at least one ofthe list information regarding an AP which should respond to the proberequest frame and the list information regarding an AP which should notrespond to the probe request frame is included in the probe requestframe, when the AP corresponds to the list regarding an AP which shouldrespond to the probe request frame, the AP transmits the probe responseframe to the station, and when the AP corresponds to the list regardingan AP which should not respond to the probe request frame, the AP doesnot transmit the probe response frame to the station.
 22. The method ofclaim 15, wherein the probe response frame is discarded based on theinformation regarding a response reception time.
 23. The method of claim15, wherein in case the max channel time is lapsed, the AP does nottransmit the probe response frame to the station.
 24. The method ofclaim 15, wherein in case the AP does not satisfies the preferenceinformation, the target AP does not transmit the probe response frame tothe station.